Fire control directors

[Guest]

Capital ship fire control directors seems to be organized very different across different navies. For example, American director seems to be based on a single rotating structure the contains a short base range finder like device, with no other clear directing optics. The primary optical range finding seems to have been done through the long base range finder in the turret. British range finders seem to also be based on a single rotating struture, also with a short based range finder, but has apertures on the front for additional optics. Again much more effective long base range finder are only to be found in the main gun turrets. German and Japanese directors seem to be based on multiple structures. There is a separate rotating component containing a long based range finder, usually the same base length as what is found in the main turret,, and then there is a separate non-rotating component which houses one or more director optic that uses one or more small rotating periscopic optic turret on top to track the target.

Are there any illustrative documentation detailing exactly how fire control is performed with each of these setups? They are likely to be very different.

[Werner]

Your analysis of the American system is inaccurate. I suggest you refer to the charts in Friedman's US Naval Weapons. The US system was organic, with range and bearing sources at the mastheads and at some turrets. This information was transmitted to the central station low in the ship where gyroscopic data (level and cross-level as well as rates of change for turn and speed), wind, ship's speed and so on was fed into the main fire control computer. Later, Radar range and bearing were fed into this computer, but the results were transmitted electrically to the turret hydraulics to effect aim.

The computer (which was mechanical-analog) frequently had several cams to accommodate heavy and light shells and full or reduced charges.

Turret directors were backup instruments as well as auxiliary inputs, and they were frequently omitted or removed as the Radar era progressed.

[Seasick]

The German and Japanese systems were less advanced. The Germans had very good optics but the radar was less reliable. The USN was more confident in its systems; though the 16 inch guns could take direction from either the Mk37 or Mk38 fire controls.

[Werner]

The USN was more confident in its systems; though the 16 inch guns could take direction from either the Mk37 or Mk38 fire controls.

The switchboard which routes outputs from the computers to the various 5-inch and 16-inch turrets is a sight to behold! Row upon row of large switches about 6-inches in diameter so the combinations can be immediately verified even in smoke or low light conditions.

For reliability's sake every system is in duplicate in primary and secondary stations.

[Tiornu]

See the recent articles on gunnery in Warship International.

[ar]

Friedman's new book, which will be out in January should help a lot.
One of the problems that is almost never metioned is that of vibration. The battleship Massachusetts suffered badly from this during the engagement at Casablanca. American battleships were more prone to this than RN battleships, because the former had tall towers for the main director, the tower acted a little like a tuning fork allowing vibration from the main guns tp travel up the tower and effect the director and fire control radar, while the RN had block structures, and although they to had vibration problems, it was not to the same extent.

[Werner]

I wonder if this would have remained a problem for the USN ships had the mass of the tower been anchored in the lower member of the ship's girder instead of the upper.

[bengtsson]

I wonder if this would have remained a problem for the USN ships had the mass of the tower been anchored in the lower member of the ship's girder instead of the upper.

Maybe Werner, whenever you change the length of the freestanding sides, you would change the resonant frequency of the structure.
I've read off and on over the years about vibration turning up as a real problem under high speed conditions. As one would see in battle, but maybe not at gunnery exercises.
Nice picture Werener! Don't you just love the old stone age technology I'll never forget my first fire control lecture when we had a look at the mechanical parts going into making the analog computer controlling our old Fletcher class DD's five inch guns. As an electronics/sonar tech. I couldn't help but laugh. Still it did the job in WWII


Bob B.

[Guest]

You all miss the point. I am focusing on the role of various optics. US and British fire control directors possess only short based range finders, so the most accurate range finding information necessarily comes from somewhere else, namely the long base range finder in the main turrets. US system appears to have no optics in the director other than the range finder. So it appears that the range finding optics is transmitting bearing, bearing rate, and some information on the range, although exactly what ranging information is not clear due to clearly overlapping range finding duty between the director and the main turret. The British system has sighting ports on the director, so there must be other optics besides the range finding optics. What are their roles? Do they merely help to bring the director onto the target or do they also transmit other information? In any case the directing optics seem to be constrained to bear in the same direction as the range finding optics.

German and Japanese directing station on the mast head all involve separate director optics and range finder in completely different structures. There is a separate, independently traversing long base length range finder, equal to what is in the main turret and thus capable of providing ranging information on a par with what can come out of the turret range finders, and separate independently rotating directing optics. In many cases there are multiple identical directing optic heads in each director station that can simultaneously track multiple targets. That they are indeed used to track multiple targets is attested by Bismark's survivors, who indicated that the British cruisers and battlecruisers are simultaneously tracked from the director station using different director optics during the Hood engagement. Indeed these indpendent director optics heads can not all be brought onto the same bearing due to mutural masking or masking by nearby structures. Although there are multiple identical directors in each director station, range finding can only be done one at a time as there is only one range finder at each station.

[Guest]

Your analysis of the American system is inaccurate. I suggest you refer to the charts in Friedman's US Naval Weapons. The US system was organic, with range and bearing sources at the mastheads and at some turrets. ......

Every diagram of WWII era captial ship fire control process I've seen shows multiple "organic" data acquisition, regardless of which country and which ship. So I think it is safe to say the word "organic" is hype that does not really describe any specific distinguishing features. AFAIK, the main turrets on new USN battleships didn't loose their long based range finders through the war. In any case, as far as optical range finding goes, the turret range finders, with their much longer base length, must be more accurate and form the primary source of ranging information prior to radar.

[bengtsson]

You all miss the point. I am focusing on the role of various optics. US and British fire control directors possess only short based range finders, so the most accurate range finding information necessarily comes from somewhere else, namely the long base range finder in the main turrets. US system appears to have no optics in the director other than the range finder. So it appears that the range finding optics is transmitting bearing, bearing rate, and some information on the range, although exactly what ranging information is not clear due to clearly overlapping range finding duty between the director and the main turret. The British system has sighting ports on the director, so there must be other optics besides the range finding optics. What are their roles? Do they merely help to bring the director onto the target or do they also transmit other information? In any case the directing optics seem to be constrained to bear in the same direction as the range finding optics.

German and Japanese directing station on the mast head all involve separate director optics and range finder in completely different structures. There is a separate, independently traversing long base length range finder, equal to what is in the main turret and thus capable of providing ranging information on a par with what can come out of the turret range finders, and separate independently rotating directing optics. In many cases there are multiple identical directing optic heads in each director station that can simultaneously track multiple targets. That they are indeed used to track multiple targets is attested by Bismark's survivors, who indicated that the British cruisers and battlecruisers are simultaneously tracked from the director station using different director optics during the Hood engagement. Indeed these indpendent director optics heads can not all be brought onto the same bearing due to mutural masking or masking by nearby structures. Although there are multiple identical directors in each director station, range finding can only be done one at a time as there is only one range finder at each station.

So really you're asking about a separate system for taking target bearing and a separate system for taking target range. I would think one separate optical system for holding the bearing of the target desired and the guns following that bearing taker. The range finders that would bear on the target should then follow the target and bearing indicator and pass their ranges on that target down to the trasmitting room. Right? The more range takers the better for the computation.
A photo in one of my books on Japanese destroyers clearly shows the director in an open state, with the range finder situated up and behind two men in a forward position with large binoculars hard mounted. I assume the two forward men indicate target bearing and the back guy is taking the range.

Bob B.

[Tiornu]

Longer bases are certainly peferred for finding the range, but the differences aren't that significant. For example, Yamato's estimated error in ranging at 35,000yards would be +/- 229 yards; Iowa's would be +/- 275 yards. Obviously one is better, but neither is as large as a pattern size.

[RNfanDan]

I'd like to gently nudge you guys back a bit, as this thread seems to have veered off track just a little.

The topic was fire control directors, not rangefinders. Range information is just one input to a director control system.

Thank you...

[Werner]

In any event, the range finders in the turret hoods are very low to the sea and certainly useless much beyond 8-10km no matter what their base. This is confirmed by their utter dismissal by Friedman in Weapons.

As early as 1920 the USN considered the range finder bracketed to the aft side of the superstructure on Michigan 'useless', and tended to disregard low-placed instruments as an emergency backup only.

No doubt the American system in the period of 1920-1930 was superior to all others because personnel did not have to compensate for roll and pitch of their own ship, thanks to the work or Elmer Sperry. The USN also shifted at this time from the "coincidence" system, which relied on good lighting and focus on the target, enough to identify detail on the hull, to the German "stereoscopic" system, which places more reliance on the human mind's ability to naturally perceive the distance to objects near-at-hand and compare them to similar range marks projected into the field of view. The base width of the rangefinder is much less critical for parallax to work in a skilled operator. Another way to think of it is the latter is creating a synthetic aperture of the width of the instrument, but the former isn't. Instead, it's overlaying the images into a double exposure.

Like any system, the fire controls tended to be sensitive to input saturation. Automation via a stable element is a key advance not apparent from the outside looking in. The fire control computer is a second key advance, relieving the fire control team from a tremendous amount of manual plotting, calculation and the use of special slide rules like the Dumeresque or it's descendant, the Pollen Table, which substituted some calculations for an automatic estimate, thus freeing the operators to pay more attention to other, more significant inputs.

Like the USN's covert support for the diesel industry in the 1930s, the calculating industry was supported in the 1920s and 1930s, especially by grants to automate the decennial census required by the US Constitution. The USN saw this automation as a way of advancing an art which was crucial to director fire.

[Guest]

I like to think for myself about whether a proposition is reasonable. I do not accept Friedman as a particularly authoritative source on anything other than lineage of documents.

[bengtsson]

I'd like to gently nudge you guys back a bit, as this thread seems to have veered off track just a little.

The topic was fire control directors, not rangefinders. Range information is just one input to a director control system.

Thank you...

Maybe we should look more closely at what a fire control director really amounts to as being seperate from the fire control computer down in the transmitting station below decks. The director obtains the inputs for the fire control computer and sends them down to the transmitting station where the solution is made and passed up to the guns in the form of elevation and training information. The director indicates the target selected and the guns follow the director and hold on that point the director chooses ,then the range and bearing information, plus course and speed estimates are sent down to the transmitting station. The solution is sent up to the guns, the trainers follow the pointers and when on point the guns are free to be fired. At least that is how I understand the process.
The question was about what the directors actually contained by way of optical devices. And why some directors seem to have just range finder openings and others have openings for other optical instruments. In my reading, the directors also contain the spotters who control for fall of shot and the over or under / left or right corrections go from the spotters down to the transmission station as well. So I can see a range taker at his range finder, a spotter at his binoculars and the original director control officer with his binoculars holding the target desired to be engaged. So wouldn't it be at least three optical instruments to the average director?
I'm no expert for sure so go easy if I am wrong about something , but this is how I understand the system. Are all dirctors the same?

Bob B

[Guest]

It seems to me that the fire control computation involves the following steps

1. Keep a cross hair on target to get a continuous plot of the target's relative bearing in relation to one's own ship.

2. Use range finder to get a continuous plot of the target's relative range from one's own ship.

3. Plot relative range against relative bearing to get a plot of the relative position of the target on 2D sea surface in relation to one's own ship.

4. Plot one's own motions in the 2D sea surface and incorporate the result into the plot of the target's relative position to obtain a plot of the target's absolute position in 2 D sea surface.

5. Determine when a salvo can be fired, and use the plot of the target's absolute positions to predict where the target would be when the next salvo would be able to land on 2D sea surface.

6. Incorporating factors such as shell type, powder characteristics, and atmospheric characteristics to compute the bearing and elevation of the guns required to put the salvo at the predicted location of the enemy.

Judging from the photos, the director instrument with the optical heads on the German and Japanese systems were very substantial instruments, much more elaborate than merely observational periscope for putting the cross hair on target. They have a big file cabinate sized console below the optics head with dials, hand wheels, and several different eye pieces along with seats for several observers to look through them at the same time. So it seems to me that they must perform a substantial amount of plotting and computation functions.

If each director instrument on German and Japanese ships can perform some plotting computations by itself, then it seems that they could continuously maintain partial plots are solutions to multiple targets at the same time because they have multiple director instruments at each station.

American directors seems to be contained in a single rotating masthead structure that is substantially smaller than the combined volume of separate director and range finder structures on German and Japanese ships. There also seems to be no optical instrument that I can see besides the range finders. So it seems to me the American instrument uses the bearing rates of the range finder itself to compute the bearing plot to target. So each of the 2 directors could only support partial or complete solutions to one target.

Just like the American system, there are also big fire control computer stations below armored deck on German and Japanese ships. Although photos show main German and Japanese fire control computers to look extremely different from American computers. American computers look like a bank of high-voltage electric switches. German and Japanese computers look more like large consoles with seats around them, dials and hand wheels around them, and several large mechanical chart plotters spaced around the outter perimeter. I don't know what British Admiralty fire control table looks like. But I think one might suppose the American, German and Japanese main fire control computers are not alike in design, and probably not alike in the range of function each performs below the armor deck versus at the masthead.

So I am curious about what computational function is done there, versus what is done high up inside the big director instruments on the mast head.

I will guess that American system uses the masthead instruments solely to get raw bearing and ranging information by keep the cross hair on target and get its range. All raw information are then transmitted directly to the below deck station, which then performs all the plotting and computing function right from range and bearing keeping to firing solution.

German and Japanese instruments splits the plotting and computation between the director optical instruments on the masthead and the computer below deck. I will further guess that each director instrument on the German or Japanese system maintains its own bearing plot inside its cabinet sized console. Given the size of the central turret on Japanese and German range finders, I will also guess that the range finder also plots the range right inside itself on the masthead. The plots are then transmitted to the computer below deck, which then incorporate ship's own course and speed and computes a firing solution.

[Werner]

Friedman says that the US main battery director was an anachronism, unnecessary at the ranges and conditions the USN expected to fight. It survived only as an economy, originally thought to combine the functions found in the armored spotting glass and range finder. It was not needed because of the combination of stable element, fire control computer and aerial spotting from floatplanes. He points out that the last US cruisers (Worcesters) had the computer and all the below-decks pieces, but no director tower. Only Radar was provided for surface fire.

[Werner]

• The Mark 1 Fire Control Computer
  by Gene Slover @ Navweps
  
  Overview
  
  In the early 1930�s Ford Instrument Co. introduced the Mark 1 Fire Control Computer. This computer was a purpose-built computer of the electro-mechanical kind, its output being analog in nature.
  
  In my opinion, two important developments made the Mark 1 possible:
  
  One was a device called a Selsyn which was developed about 1925. This was the first really good device that could transmit and receive electrically the mechanical position of anything.
  
  So with this device director information could be transmitted electrically to a remote location, such as a computer. The computer could transmit its output electrically to a gun mount or turret.
  
  The other device that was really important was the mechanical rate integrator. With this device, time and position, for the X, Y and Z axes, could be integrated together.
  
  Integrating time and position together with the other components of the FC problem could predict a future position.
  
  This put Ford Instrument Co. and the USN on the road to producing the finest FC System of the time.
  
  At this time all of the equations and formulae were well known that were necessary to solve the FC problem to the target. This was incorporated into the Mark 1 computer.
  
  Ballistic calculations were available on all sizes of guns in a horizontal plane. I do not know which gun was used for the ballistic calculations for the first Mark 1 computer.
  
  As I understand it, the original Mark 1 computer could solve only the X and Y coordinates of the FC problem.
  
  
  The Mechanical Rate Integrator
  
  The mechanical rate integrator consisted of a plate about 1/2� thick and about 6� in diameter. A 1� diameter ball. A 1/2� thick plate, 1� in diameter. A moveable carriage to hold the 1� ball and 1� plate.
  
  The 6� diameter plate was rotated at a constant speed, to provide a time constant.
  
  The carriage held the 1� diameter ball, and the 1� diameter plate. The carriage pressed the 1� diameter ball against the 6� diameter plate with a force of 6 pounds.
  
  The home position of the 1� ball is the center of the 6� plate. At this position there is no output, the 1� ball has no rotation imparted to it at this point. The 1� plate collects any rotation of the 1� ball for transmission elsewhere.
  
  The carriage constantly receives a positioning input to drive the carriage to position the 1� ball in the center of the 6� plate for zero output. This positioning signal is also time constant.
  
  If there is any movement or change in the coordinate that the integrator is to calculate, X, Y, or Z, this change is applied to the carriage which moves the 1� ball off of the center of the 6� plate. The larger the change, the further the carriage moves the ball. The maximum movement being 3� which would put the ball at the edge of the 6� plate, where the output speed of the 1� ball would be at the maximum possible.
  
  As long as the coordinate is changing, the carriage will continue to receive an input signal that keeps the ball off of the center of the 6� plate. If the coordinate stops changing, then no input is available to drive the carriage away from the center of the 6� plate. This constant input that the carriage is continuously receiving then drives the carriage and ball back to the center of the 6� plate. Only at that point is there is zero output from the 1� ball.
  
  
  Memory
  
  The Mark 1 has no memory, so it does not remember any past event(s).
  
  The computer is only interested in current events.
  
  Through the use of the mechanical rate integrator, which is the computer�s crystal ball, the computer can predict the future. The future position of the coordinates that it is currently measuring.
  
  
  The Ballistic Section
  
  The ballistic section of the computer contains all of the ballistic information for the weapon that the computer is to control.
  
  All of this information is based on new gun performance and new gun initial muzzle velocity (IV).
  
  This section of the computer has one manual input, Current IV.
  
  Bore information is used to manually compute bore wear, so that you can manually produce a current IV for the gun.
  
  Available weather information, plus current bore wear, produces the current IV for the gun.
  
  The weather information is measured on an hourly basis. From this you calculate and manually input the current IV to the ballistic section of the computer.
  
  
  Differentials in the Computer
  
  The differential is widely used in the Mark 1. The differential is like a car differential except that it is small enough to hold in your hand. The ones in the Mark 1 have a 2:1 gear ratio, which means that the drive shaft input requires 2 turns in order to get the wheel shafts to make one turn.
  
  Just like a car differential, if you hold any one shaft, and turn one of the other shafts, the third shaft turns in response.
  
  If you hold the drive shaft input, and turn one of the wheel shafts, which are opposite each other, the opposite one will turn.
  
  The differential was used in places where there was a need for one shaft to have an input from two places.
  
  For example, the target bearing from the director is fed into one of the shafts of the differential � in this case that would be one of the wheel sides. The opposite shaft might be connected to a manual knob that would be to enter an offset bearing. The drive shaft side, which is going to turn at 1/2 speed of the director input because of the 2:1 gear ratio, then drives some aspect of the computer gear and cam mechanism. If the output of the drive shaft side needs to turn at the same speed as the input shaft, a set of 2:1 gears does this.
  
  The hand knob manual input, for offsetting bearing is held by a friction disk to the computer case, so the knob requires some effort to turn it. This ensures that the input from the director bearing goes out via the drive shaft side of the differential and not back out through the hand knob. There is also a friction clutch in the shaft and gearing between the manual input knob. This slips if the mechanism reaches its maximum travel and encounters a mechanical stop. This is to prevent damage to the internal parts of the computer.
  
  The carriage of the mechanical integrator needs an input from two shafts. One is the time constant that drives the carriage to the center of the disk. The other input is bearing or range that moves the carriage away from center.
  
  
  Looking Inside the Computer
  
  The computer is about 3 ft wide, 4 ft tall, and 6 ft long. Looking inside the Mark 1 was like looking into a fine mechanical watch. Everything was very compactly designed and organized. The first look is completely mind bending, making one wonder what is all this stuff and how does it work? How could anyone ever have put together something like this and made it work? Especially in 1930.
  
  The components are so packed inside that you can only stick your finger into the components. There is not enough space for your hand or arm to fit inside. All of the components are either parallel or at right angles to each other.
  
  Each component part is built like the mechanical integrator, all in one piece. The component parts are all reasonably strong and the mounting plate it is built on is usually a sheet of steel 1/2� thick. The component parts are usually mounted using 4 to 6 1/4� socket head cap screws. You do not have to be very careful with these parts, as they do not damage easily.
  
  The component parts have input and output gearing and shafting which connects them to the other component parts of the computer. Most of the shafting is 1/4� diameter, some is a little larger. The shafting is held in place by ball bearings, which are held in place by various mounting blocks. Miter gears are used to make 90 degree turns of the shafting which allows them to connect to the various component parts.
  
  A tool box is furnished with the computer. This tool box contains the special tools necessary to reach inside the computer. Some of the tools have small lights on the end of a rod about 3 ft long. The light can be swiveled on the end of the rod, so you can put it far enough into the computer to see with. Other tools are 3 feet long with 90 degree bevel gears at the end. This might hold an Allen wrench, so you could turn an Allen screw or socket head cap screw deep in the computer. As you can guess, working on the internals of the computer while the ship was moving was quite difficult.
  
  
  The Miter Coupling
  
  The miter coupling is used to make adjustments to the input and output shafting of the components.
  
  This coupling consists of two parts, or halves, each of which are mounted on the end of a shaft. The miter coupling connects two shafts together. One of the coupling halves has teeth on its outer diameter, sort of like the teeth on a gear. The other half of the coupling, mounted on the other shaft, has a screw in it that its threads engage the teeth of the gear on the other half of the coupling that is mounted on the other shaft. Turning this screw then moves the coupling halves in rotation, with respect to each other. This, then, is the mechanical adjustment that aligns the shaft input, or output, to and from the different mechanical components. Once the adjustment is made, there is a locking screw in the miter coupling that when tightened does not allow movement of the adjusting screw. This then keeps the adjustment from changing.
  
  
  The Remote Computer Inputs
  
  The original Selsyn devices were about 8 to 10 inch diameter and were also about that long. Even though they were large, they did not have much power to drive or position anything other than a very light load.
  
  So the Selsyn was sort of re-invented, and made smaller, down to about the size of your fist. These were re-named Synchros, and the term stuck.
  
  The synchro in the Mark 1 positions cams, which close and open electrical contacts, which in turn, start, stop and run servo motors. The servo motors actually provide the power to turn, set or adjust the various elements in the computer, all as accurately as if the servo had actually positioned the element in question.
  
  This gave, or gives, the computer the ability to receive remote inputs of range, bearing, and elevation to the target, from a remote director.
  
  True North is an input from the ships Master Compass. It is also transmitted electrically and received by a synchro, which inputs True North into the computer.
  
  The ships heading or course is another input to the computer. This allows the computer to keep up with the ships relative heading with respect to True North.
  
  On the computer there is an indicator which is an outer ring of a dial. This dial shows True North. Inside this dial there is another dial, which shows the ship�s heading. This dial also has an outline of a ship drawn on it, with the bow at zero degrees. When you look at this dial, you do not have to look for the zero to know which way the ship is heading. All you have to do is read the picture of the outline of the ship.
  
  
  The Correction for Coriolis Effect
  
  The computer needs to know where True North is with relation to the ship�s heading.
  
  This information is necessary because of a naturally occurring thing called Coriolis Force.
  
  Coriolis Force is an apparent force that as a result of the earth's rotation, deflects moving objects, (as projectiles or air currents), to the right in the northern hemisphere and to the left in the southern hemisphere.
  
  The computer does not correct for Coriolis Force, but rather for Coriolis Effect.
  
  Coriolis Effect is the apparent deflection of a moving object that is the result of the Coriolis Force.
  
  The weight of the projectile and its speed must be known to correct for this effect.
  
  The computer must also know the ship�s latitude. This is because at different latitudes, the effect from Coriolis Force is different.
  
  The direction the projectile is fired in with relation to True North must also be known. This is because firing at or in different bearing directions with relation to True North the Coriolis Effect is different.
  
  
  The Horizontal Plane Input
  
  The FC Directors on a Battleship are about 100 feet above the water line. As the ship rolls and pitches, the director is tilted out of the true horizontal plane, of or with the level of the ocean. The director is sort of like mounted on a vertical stick about 100 feet tall, with its pivot point at a point below the water line. So as the ship rolls and pitches, the FC Director swings back and forth at the top of the 100 foot tall stick. Since the director is locked on and tracking a target, this swinging back and forth is being transmitted to the computer as changes in bearing and elevation of the target. This is actually false information, because the target is not making these moves.
  
  To correct this false information, a true horizontal plane is generated by a device called a stable vertical on Battleships and Cruisers. On Destroyers, a stable element provides this information. There is actually very little difference in the two devices.
  
  The true horizontal plane generated is transmitted mechanically to the computer. The stable vertical or stable element sits about 18� away from the computer, and mechanical shafting transmits the true horizontal plane directly into the computer.
  
  Inside the computer, this input is applied to the director inputs for bearing and elevation by the mechanical differentials. They add or subtract as necessary from the FC Director inputs, to convince the computer that the FC Director is not moving and is staying in a vertical and horizontal position with relation to the ship and the target.
  
  
  True North and the Mark 1
  
  The Mark 1 uses true north to keep up with the ships heading and to keep up with the target in relation to the ship and true north.
  
  It is necessary to keep up with true north, the ships heading, and target bearing, in order for the computer to make the correct adjustment to correct for Coriolis effect.
  
  The movement of the ship in course and speed are transmitted into the gun, so when the gun is fired, this movement is imparted to the projectile, and becomes a part of it�s flight pattern or trajectory.
  
  The computer then corrects the position of the gun, to remove this imparted motion in the projectile, so that the projectile will land on target.
  
  If the target is moving, for the computer to correctly calculate the true course and speed of the target, true north must be known.
  
  
  Target Solution
  
  As the FC Director continually inputs bearing and range information into the Mark 1 computer, the computer is continuously producing an output to position the guns to a position that will hit the target.
  
  So if the target is stationary, accurate gun fire can be done, or commence, at any time because the computer does not have to predict a future position of the target. The FC solution is instantaneous, with a stationary target.
  
  If the target is moving, it will take the computer a maximum of 30 seconds, to predict the course and speed of the target, from the time, or moment of target acquisition.
  
  If the target changes course or speed, it will take the computer only a few seconds to come to a perfect solution for the new course and speed, but not an entire 30 seconds, as it needs for a new target solution.
  
  
  Range and Bearing can be Manual Inputs
  
  Range and bearing to the target can be put into the computer manually, without using the FC director.
  
  The computer has mechanical rate integrators that can correct the manual input of range and bearing for the course and speed of the ship. The ship can then make any change in course and speed but the range and bearing manually set into the computer are automatically reset by the mechanical rate integrators. With these inputs, the computer can keep track of the target's position relative to the firing ship at all times.
  
  The manual inputs of range and bearing are normally used in shore bombardment, and in particular when there is no line of sight between the FC director and the target. The actual range and bearing figures used usually come from CIC (Combat Information Center).
  
  They can, however, be transmitted from a lookout or any other place directly to the FC officer in the FC plot room with the computer. In which case the information might just be their best guess. However, after seeing where the rounds impact in relation to the target, offset corrections can be easily made and the second salvo will be much closer to the target..
  
  
  The Starshell section
  
  The starshell section of the computer allows you to take one gun mount or turret and reposition it to fire starshells for target illumination for the other weapons.
  
  This section of the computer takes the generated or computed firing solution and allows the operator the control necessary to offset the gun from the target position.
  
  Offsets can be set into the starshell section to correct for range, bearing, elevation and the prevailing wind so as to correctly position the exploding starshell.
  
  
  A & B Tests
  
  The A and B tests checked the computer for accuracy.
  
  The A tests checked the input information against the computed output information. These tests determined if the computer could correctly solve a particular FC problem.
  
  There was a table of about 50 FC problems with the input figures for each problem. The table also contained the output figures for each problem and the allowable tolerances for error of each problem. The operator entered the input figures into the computer and checked that the output figures agreed with the table values within a small tolerance envelope.
  
  The tests checked the computer for many bearing and range inputs, so as to make sure that the computer could solve correctly a firing solution to any target.
  
  These test were run, let�s say, on Monday, Wednesday, and Friday. Usually about 6 tests on each day. So about every 30 days, the complete set of A tests were completed.
  
  The B tests checked the mechanical rate integrators, to make sure that the computer could apply time to the computer inputs and correctly predict the present course and speed of the target and produce a gun output position for the future position of the target.
  
  The B tests were run on the days between the A tests. Like the A tests, a table gave the inputs to be used and what the output solution should be, and gave the allowable tolerances for error.
  
  These B tests, like the A tests, were to check the computers ability to solve any FC problem at any range and bearing.
  
  
  Ladder Salvos and Alignment
  
  Once the Mark 1 computer came into being, the use of ladders for ranging went out the window. As long as there was a line of sight to the target or if the correct grid coordinates of a shore bombardment target existed, the Mark 1 eliminated any need for �ranging ladder salvos.�
  
  In test firings, or firing practice, ladders were still used to teach how to use ladders to obtain range.
  
  Firing practice trained the crews of the entire ship in their respective jobs.
  
  Firing practice checked out all of the equipment, to make sure that all was in working order.
  
  Firing practice checked battery alignment and the pattern of the shells in the target or impact area.
  
  If the pattern size, range, or bearing was wrong, at the first opportunity, battery alignment was done to correct the errors.
  
  Offsets, set into the computer, could correct for bearing and range misalignment, and the computer would keep these corrections.
  
  The computer could not correct for pattern errors. If one gun was off it had to be manually corrected in battery alignment.
  
  
  Shore bombardment with the Mark 1 computer.
  
  A bridge is a target 10 miles inland and out of the line of sight of the firing ship. Through the use of spotters, range and bearing, usually derived from a grid map, are transmitted to the firing ship.
  
  CIC provides Fire Control with the range and bearing to the target. The spotter gives corrected information to the firing ship, if range and bearing corrections are necessary, to adjust the fire to hit the target.
  
  CIC records ship position and range and bearing to the target as each salvo is fired. Once correct range and bearing to the target are obtained, which is evident by your shells hitting the target. CIC records the correct position of the target on the grid map.
  
  This ship, or any other ship, can come back a year later, and with the previous CIC records, can open fire and hit the bridge, with no spotting necessary.
  
  Using the Mark 1 computer to amass fire.
  
  Accurate fire on a single target, from several ships became possible, with the Mark 1 computer.
  
  With one ship firing on a target, that ship transmits relative range and bearing from it to the target.
  
  CIC of each ship, then uses relative range and bearing of the firing ship, to provide their Fire Control plot room, with their own range and bearing to the target.
  
  The ships do not have to be in a battle line, they can be in any position, although steaming in a battle line, is what was generally done.
  
  
  The Mark 1A Computer
  
  About 1935 Ford Instrument Co. added the ability to the Mark 1 computer to compute rate changes in elevation or the z coordinate.
  
  The Mark 1 could compute in elevation, it just could not compute rate changes in terms of elevation. It knew if the target was on top of a mountain, but that was about all it could do in elevation calculations. It could not tell if the target was moving in elevation. The ballistics cut for the Mark 1 were only for surface-to-surface firing and there were no provisions for the surface-to-air calculations needed for the anti-aircraft role.
  
  The Mark 1A overcame this little problem.
  
  It also changed the maximum allowed target speed of about 200 knots up to about 450 knots.
  
  The new computer design became the Navy�s first Dual-Purpose computer, as it could handle aircraft targets as well as surface targets.
  
  When coupled to the 5�/38 gun, the Navy now had the finest anti-aircraft fire control system in the world. No other Navy could match this FC system through out World-War II. The British purchased this system for use on their ships, but only a single anti-aircraft cruiser actually saw service with it during the war.
  
  The Mark 1A dual purpose computer together with the 5�/38 in single and twin mounts were deployed on almost every USN ship from destroyers through battleships and carriers by the end of the war.
  
  The Mark 1A is what made the 5"/38 the most successful dual-purpose gun of the war as it gave those guns true anti-aircraft capability. No other nation came close to developing the computer-gun combination so well.
  
  As the Jet-age came about in the late 40�s, the computer was modified to allow maximum target speed about 650 knots. Our jets were approaching the breakneck speed of 550 knots. There were many who thought that the sound barrier would not be broken.
  
  As far as I know the only ballistics that were ever cut and installed in the Mark 1A were for the 5�/38 gun until just about wars end. At that time, the 5�/54 was being introduced on the USS Midway class carriers. This weapon had different ballistic characteristics and needed different computations than did the 5"/38.
  
  
  Reliability
  
  There was no scheduled maintenance, recommended or performed on these computers. They were quite reliable and lasted for years without breakdowns.

http://dcoward.best.vwh.net/analog/ford.htm

[Guest]

If I guessed correctly that German and Japanese fire control separates plotting function from computational function, and incorporate ranging and bearing plotting functions directly into the optical instruments responsible for directly accessing these data, then I think I have a more fundamental explanation for the difficulties they've encountered in using radar for fire control. The reason they have trouble with radar fire control is their fire control computer has no native capability to maintain plots of range and bearing history for the purpose of anticipating future range and bearing. They rely on the separate instruments on the masthead to maintain the plot and are mere consumers of range and bearing plot. If there is no optical solution to the target, then they loose the integrated ability to plot. If all they have is range and bearing data from radar, they would have to extemporize the plotting functions.