Royal Navy Dido class Light Crusiers

[bengtsson]

Namned Cruisers 92 Destroyed - 23 Probable - 49 Damaged

Unamed Cruisers 5 Destroyed - 1 Probable - 2 Damaged

Didos 15 Destroyed - 1 Probable - 7 Damaged

roughly speaking

"Ensign 2 Dido Class Cruisers"

This does match the figure in "Cruisers in Action" P. Smith & J. Dominy

They give 97 total Didos getting their 15 out of the total.

For sure, who knows how many were from main armament. Didos may have only one or two by the 5.25 inch guns. The 2 pdr being most likely the agent of distruction.
Not many for sure. Of course they never saw the scale of air attack that occured in the Pacific. And German planes were not so easy to bring down as Japanese flying gas bombs!

Bob B.

[Werner]

I have not seen any figures, but I would very much doubt that the main armament of cruisers shot down many aircraft. The effectiveness of the twin 4" and the 5.25" would have been in breaking up attacks at long, to medium range. A significant advance was made when ships were fitted with barrage directors coulpled with type 283 radar. Named the Auto Barrage System.

Where the Atlanta is concerned, the 5-inch went from being the poorest performing US AA gun in 1942 to the best by 1944, thanks to the influence ("VT") shell. I imagine the Didos would have benefitted similarly from an influence shell. Was one produced before War's end?

[Foeth]

the 5-inch went from being the poorest performing US AA gun in 1942

Really? I always thought the 5-inch gun itself was pretty decent. (plus, only a 2% hit rate with the VT fuze. Ah, even Richard Feynman confessed he thought balistic calculations were too difficult).

[Werner]

I have to pull out Friedman who went into the VT fuse in some detail for numbers, but the mechanically timed gun did not perform as well as 1.1 and 20mm. After the VT shell went to sea in 1943 (first kill was by Helena), the situation was totally reversed in favor of the 5-inch. By 1945 there was impetus to put a VT mechanism in smaller guns, which led to the post-war 3-inch/50 twin and singles of the '50s, which was the smallest shell BuOrd could stick the VT mechanism into.

There was also a latent disgust with so much weight taken up in machine cannons which had a 5000 yard maximum range, and were therefore strictly defensive in nature.

[ar]

Namned Cruisers 92 Destroyed - 23 Probable - 49 Damaged

Unamed Cruisers 5 Destroyed - 1 Probable - 2 Damaged

Didos 15 Destroyed - 1 Probable - 7 Damaged

roughly speaking

"Ensign 2 Dido Class Cruisers"

This does match the figure in "Cruisers in Action" P. Smith & J. Dominy

They give 97 total Didos getting their 15 out of the total.

For sure, who knows how many were from main armament. Didos may have only one or two by the 5.25 inch guns. The 2 pdr being most likely the agent of distruction.
Not many for sure. Of course they never saw the scale of air attack that occured in the Pacific. And German planes were not so easy to bring down as Japanese flying gas bombs!

The scale of air attack in the Med for all of 41/42 was as intense as any in the Pacific. Two out of many examples would be Crete and Pedestal. The attacks during the latter lasted four/five days and MUST have involved hundreds of enemy sorties. Perhaps someone familar with aircraft can supply details?

Bob B.

[ar]

VT shells were used by the Didos in the Pacific late war but I have no more data than that.

[RNfanDan]

Ah, even Richard Feynman confessed he thought balistic calculations where too difficult

What a mind he had, and the common sense to use it correctly! We need more around like him, today.

[Werner]

Ah, even Richard Feynman confessed he thought balistic calculations where too difficult

What a mind he had, and the common sense to use it correctly! We need more around like him, today.

Certainly one of my heroes. Several of his books, including Lectures on Computation sit on my bookshelf.

[bengtsson]

Scale of Air Attack in the Medit. Yes ,quite right. It was intense as can be. I guess my mind was more on the huge suicide attacks later in the Pacific war. Also the Carrier battles where naval aviators with higher skill levels were involved.
The German JU 88s were often used in large numbers and except for those with special anti shipping training proved unable to score a very high hit ratio. Though superb ship handeling was a factor as well. Even in the arctic, hours on end of JU88 bombing was not uncommon. Maybe the JU 88 itself was not a good aricraft for the anti shipping role? Anyone have a thought?

Bob B.

[ar]

Scale of Air Attack in the Medit. Yes ,quite right. It was intense as can be. I guess my mind was more on the huge suicide attacks later in the Pacific war. Also the Carrier battles where naval aviators with higher skill levels were involved.
The German JU 88s were often used in large numbers and except for those with special anti shipping training proved unable to score a very high hit ratio. Though superb ship handeling was a factor as well. Even in the arctic, hours on end of JU88 bombing was not uncommon. Maybe the JU 88 itself was not a good aricraft for the anti shipping role? Anyone have a thought?

Bob B.

Try not to get too caught up one type of aircraft. The subject is complex.

[Tiornu]

By mid-August 1945, American companies had provided 840,000 VT fuzes for the RN. An additional number of US Mk 32 VT fuzes, intended for 5in shells, went to the RN for American-made weaponry and for conversion to British ammo.
The numbers from late 1944 show a doubled kill rate for American 5in guns using VT ammo. This probably understates the difference, as other calculations show a tripled kill rate. Against the increased kill rate, the time-fuzed shell has some compensation in the distraction created by its explosion even while missing.
It's subjective, of course, but I can't see calling the 5in gun the poorest AA weapon in 1942. Though not as good as it would eventually be, it was still a capable plane-killer. I don't think it was "poorer" than the 1.1-inch, the .50-cal, or the 3in gun.

[bengtsson]

.
Shooting down aircraft seems to be more of a light AA function. 20mm, 2pdr and later 40mm were more likely to do the job. Of course the aircraft is alot closer when they open up. I've read that the main armament AA fire seemed more likely to throw off the attackers aim or will to close the target than knock them down.

The VT fuse. I've heard several different explainations about how it functioned. Was their more than one kind?

Bob B.

[Werner]

It was an electronic device (wonderful for the era) that sensed the proximity of large objects due to the subtle changes in electric field near the object. You could consider it a primitive Radar system.

The shell would explode either when it passed within the lethal radius of the target, showering the target with high speed fragments and shock effect, or when the capacitor ran out, preventing a long over from doing damage as it fell back to sea.

It's predecessor was the "mechanical time" fuse, which was essentially an alarm clock. This is the fuse that was set by one of the gun crew who took the shell and inserted it into a pipe-looking stand on the port side of the 5-inch/38 single, where a crank set the "alarm". Knowing the altitude and horizontal distance to the target, the range finder solved the time to distance problem and set the fuse to go off in the appropriate number of milliseconds. These shells also had an impact fuse.

[bengtsson]

It was an electronic device (wonderful for the era) that sensed the proximity of large objects due to the subtle changes in electric field near the object. You could consider it a primitive Radar system.

Thanks Werner, that is the explaination I have heard before. That it was some form of primitive radar detector that caused the shell to go off. Being an electronics technician myself starting with my Navy experience, I have always wondered about the VT fuse. There was no way I could figure out how a fuse sized system,at that early date,could have anything to do with even primitive radar. I plead ignorance here
Now read this that I came across recently and see what you think of this explaination.

from : "The Lexington Class Carriers" by Robert Stern pg. 100

" The first faltering step towards 'smart' weaponry came with the introduction of the proximity fuse"
This was a joint development by the British and Americans, the original work on photo-electric cell being done in the USA by Western Electric and RCA, and much of the experimental work of turning it into a useful fuse being done by Dr. Aylwin Crow in England.
The principle was that the shell was aimed so that, if it did not hit, it would miss just under the target. The shadow cast by the target would interrupt the current generated by the photo-electric cell in the fuse, which was used to detonate the shell.".

There is more that follows, but the principle is stated to be a simple photo-electric cell which is triggered by the shadow of the target. As a former ET, this system makes perfect sense to me and is within technical capabilities of the time. But this has nothing to do in any way shape or form with radar or even metal detection of any sort. I assume that after the war, further work on influence fuses would have found metal detection to be a further possible avenue for a fuse, I can't ever see a fuse of those early days able to transmit a radar signal and detect an echo.

So where does this explaination above, leave the issue of the WWII VT fuse??

Bob B.

[Werner]

IIRC, the above description does not apply to the US VT fuse.

The WW2 patent works as follows: The shell contains a micro-transmitter which uses the shell body as an antenna and emits a continuous wave of roughly 180 - 220 MHz. As the shell approaches a reflecting object, an interference pattern is created. This pattern changes with shrinking distance: every half wavelength in distance (a half wavelength at this frequency is about 0.7 meters), the transmitter is in or out of resonance. This causes a small oscillation of the radiated power and consecutively the oscillator supply current of about 200 - 800 Hz, the Doppler frequency. This signal is sent through a band pass filter, amplified, and triggers the detonation when it exceeds a given amplitude.

Before the fuze's invention, detonation had to be induced by direct contact, a timer set at launch, or an altimeter. All of these have disadvantages. Getting direct contact with a relatively small moving target is hard (even ignoring the effect of wind); to set a time- or height-triggered fuze one must measure the height of the target (or even predict the height of the target at the time one will be able to get a shell or missile in its neighbourhood). With a proximity fuze, all one has to worry about is getting a shell or missile on a trajectory that, at some time, will pass close by the target. This is still not a trivial task, but it is much easier than previous methods were.

Use of timing to produce air bursts against ground targets requires observers to provide information for adjusting the timing. This is not practical in all situations and is slow in any event. Proximity fuzes remove these problems.

The proximity fuze was invented in the UK in 1940, but developed mainly by the U.S. (with British collaboration) during World War II. Vannevar Bush, head of the U.S. Office of Scientific Research and Development (OSRD) during this war, credits it with three significant effects. It was important in defense from Japanese Kamikaze attacks in the Pacific. It was an important part of the radar-controlled anti-aircraft batteries that finally neutralized the German V-1 bomb attacks on England. Third, it was released for use in land warfare just in time for use in the Battle of the Bulge, where it decimated German divisions caught in the open. The Germans felt safe from timed fire because the weather prevented accurate observation. Bush cites an estimated seven times increase in the effect of artillery with this innovation.

[RNfanDan]

This is the fuse that was set by one of the gun crew who took the shell and inserted it into a pipe-looking stand on the port side of the 5-inch/38 single, where a crank set the "alarm". Knowing the altitude and horizontal distance to the target, the range finder solved the time to distance problem and set the fuse to go off in the appropriate number of milliseconds.

Which of course, could not be too accurate by the time the crewmen had loaded the shell and locked the breech, which could vary not only by the gun crews' speed and efficiency, let alone fatigue level. A few milliseconds in flight at shell velocities, translates to an enormous distance error for each millisecond the shell is delayed between setting and firing...little wonder they seldom hit anything!

[Timmy C]

There is more that follows, but the principle is stated to be a simple photo-electric cell which is triggered by the shadow of the target. As a former ET, this system makes perfect sense to me and is within technical capabilities of the time. But this has nothing to do in any way shape or form with radar or even metal detection of any sort. I assume that after the war, further work on influence fuses would have found metal detection to be a further possible avenue for a fuse, I can't ever see a fuse of those early days able to transmit a radar signal and detect an echo.

So where does this explaination above, leave the issue of the WWII VT fuse??

Bob B.

But wouldn't the PEcell be in the shell's shadow at some point before the it hits near the plane, as the shell is spinning?

[Guest]

The aim of delayed AA fuse setting before VT fuse wasn't as ambitious as actually getting the shell to explode at the actual predicted range of the target. If that were the case the slightly different amount of time it takes for the loader to manually move each shell from the fuse setter to the breach would upset the calculation and cause the initiation of shell fuse timing to be off.

The idea was for the the AA fire control to predict a 3 dimensional region in the sky, usually box or spherical shaped, which the attacking aircrafts needs to fly through to threaten the ship, and then set the pointing fuse setting direction to all guns that would bear, and get them fire at that region in the sky and ensure all the shells fired would detonate in that region.

[Guest]

There is more that follows, but the principle is stated to be a simple photo-electric cell which is triggered by the shadow of the target. As a former ET, this system makes perfect sense to me and is within technical capabilities of the time. But this has nothing to do in any way shape or form with radar or even metal detection of any sort. I assume that after the war, further work on influence fuses would have found metal detection to be a further possible avenue for a fuse, I can't ever see a fuse of those early days able to transmit a radar signal and detect an echo.

So where does this explaination above, leave the issue of the WWII VT fuse??

Bob B.

But wouldn't the PEcell be in the shell's shadow at some point before the it hits near the plane, as the shell is spinning?

No, you can use a light diffuser at the nose of the shell to average the amount of light reaching the shell from all directions.

[Guest]

The WW2 patent works as follows: The shell contains a micro-transmitter which uses the shell body as an antenna and emits a continuous wave of roughly 180 - 220 MHz. As the shell approaches a reflecting object, an interference pattern is created. This pattern changes with shrinking distance: every half wavelength in distance (a half wavelength at this frequency is about 0.7 meters), the transmitter is in or out of resonance. This causes a small oscillation of the radiated power and consecutively the oscillator supply current of about 200 - 800 Hz, the Doppler frequency. This signal is sent through a band pass filter, amplified, and triggers the detonation when it exceeds a given amplitude.

[/quote]


This suggests the VT fuse is:

1. Easily caused to detonate prematurely by someone actively sending back a powerful radio signal with the frequency to cause appropriate interference frequency.

2. Won't explode if aircraft under attack undertakes radical evasive action such that the relative velocity between the shell and the target moves the doppler frequency outside the band.

It also suggests that the Germans and Japanese didn't know that this is the principle used in VT shells else they would have developed a counter for it.