Mk71 8"/55caliber Major Caliber Light-weight Gun

[navydavesof]

Hi, guys. Captain Michael Potter, a usual contributer to this website has made some very interesting comments and observations about this weapon system in another topic thread I started about a modernized Spruance-class DD/DDG. The knowledge I have been able to acrew so far has been limited to navweapons and conversations I have had with gentlemen who were involved in the project over 30 years ago.
The thing I am very interested about is why the weapon was canceled rather than being orderd and installed aboard the Spruance-class as it was being built.
Captain Potter has apointed out that the weapon apparently sufferd from muzzle wobble causing deflection issues to the point where the rounds were being thrown too far off course. Instead of correcting this problem, the program was canceled. I would venture to say that was an excuse to kill the program and was not at all un-fixable.
Captain Potter has suggested that the barrel be braced similarly to how the gatling gun in the Block 1 through 1B versions of the Phalanx gun mount has. There is no doubt in my mind, however, that this barrel wobble can be fixed inside the mount instead of having huge stantions running out from the mount to the end of the gun barrel.
What kind of input on the problem of muzzle wobble and the Mk71 do you guys have?

[Cliffy B]

I believe it fell victim to budget cuts sadly. It would be nice if or ships were all armed with 1-2 of those sweet little 8"/55 autos. The 5" just doesn't cut it mainly due to range and ERGM never amounted to anything so it's still just a short range pop-gun. Even in the days of supersonic SSMs and the like it's still necessary to have an old reliable and mechanical deck gun in reserve for when the misses run out or all of the high tech stuff goes buggy. And yes the current 5"/54s can be operated manually albeit much more slowly IIRC.

[chuck]

...... I would venture to say that was an excuse to kill the program and was not at all un-fixable......There is no doubt in my mind, however, that this barrel wobble can be fixed inside the mount instead of having huge stantions running out from the mount to the end of the gun barrel.....
What kind of input on the problem of muzzle wobble and the Mk71 do you guys have?

What is the qualification of "My mind" that would allow "There is no doubt in my mind" to form some sort of sound basis for further discussion?

[navydavesof]

The issue to which I refer is that other gun mounts have countered for errors caused by barrel wobble and barrel whip. The Mk45 Mod4 had a similar problem, and they corrected it in the prototype mount and incorporated the correction into production mounts. These corrections were performed inside the gun house (mount) itself.
The Mk71 that was on the Hull and is in Dahlgran, which is the same one that has been used to test different stages of the ERGM, was the prototype, so any issues involved in the prototype mount could be worked out in a similar fashion as the Mk45 Mod4.
Now, to expand upon what I said about the Mk71 being used for the 5"ERGM: what they did was de-line the Mk71 barrel and put a giant sabot around the 5" ERGM round. The reason they did this was they wanted to see if the round could survive launch and fly if it were not rifled. The fatal issue behind the 5" ERGM was that the control fins could not survive the wind resistance associated with the spin of the projectile as they deployed. The wings kept breaking off. So, they fired it thoguh the smooth-bore (liner-less) 8" barrel, and the weapon worked just fine. It did not acheive its 120nm range, only 100-ish miles, but it still did its thing.
They tried LOTs of things to keep the round from spinning as it traveled through the rifling of the 5"/62caliber barrel, including races holding friction-free bearing rotating bands, but it still spun too fast and destroyed every test round.
So, I'd like to hear what the impossible thing is with fortifying the internals of the Mk71 like the Mk45 Mod4 to where you'd have to brace the barrel like that of the Block 1B Phalanx mount.

[chuck]

The issue to which I refer is that other gun mounts have countered for errors caused by barrel wobble and barrel whip. The Mk45 Mod4 had a similar problem, and they corrected it in the prototype mount and incorporated the correction into production mounts. These corrections were performed inside the gun house (mount) itself.
The Mk71 that was on the Hull and is in Dahlgran, which is the same one that has been used to test different stages of the ERGM, was the prototype, so any issues involved in the prototype mount could be worked out in a similar fashion as the Mk45 Mod4.
Now, to expand upon what I said about the Mk71 being used for the 5"ERGM: what they did was de-line the Mk71 barrel and put a giant sabot around the 5" ERGM round. The reason they did this was they wanted to see if the round could survive launch and fly if it were not rifled. The fatal issue behind the 5" ERGM was that the control fins could not survive the wind resistance associated with the spin of the projectile as they deployed. The wings kept breaking off. So, they fired it thoguh the smooth-bore (liner-less) 8" barrel, and the weapon worked just fine. It did not acheive its 120nm range, only 100-ish miles, but it still did its thing.
They tried LOTs of things to keep the round from spinning as it traveled through the rifling of the 5"/62caliber barrel, including races holding friction-free bearing rotating bands, but it still spun too fast and destroyed every test round.
So, I'd like to hear what the impossible thing is with fortifying the internals of the Mk71 like the Mk45 Mod4 to where you'd have to brace the barrel like that of the Block 1B Phalanx mount.

Perhaps the barrel wobble is caused not by any inadequacy of the mount, but by the inadequate strength and stiffness of the barrel itself? This wouldn't bee the first time when large caliber weapons designed on too stringent a weight budget proved inaccurate because the light weight barrel flexed too much in the firing process.

Could that be the reason why the solution suggested involved providing additional support to the barrel at the muzzle end with an external frame?

[navydavesof]

Perhaps the barrel wobble is caused not by any inadequacy of the mount, but by the inadequate strength and stiffness of the barrel itself? This wouldn't bee the first time when large caliber weapons designed on too stringent a weight budget proved inaccurate because the light weight barrel flexed too much in the firing process.

[/quote]

I agree, Chuck. I see where you're coming from. This might be. I know the barrel of the Mk71 was a different design than those of the of the Des Moines-class. If the weapon went into production, I know that it would have been fitted without a loose-liner, a monobarrel. It would have been all one piece. In the case of the inaccuracy being caused by a weak barrel, I wonder if the extra steel in place of the liner would have added enough strength to reduce if not remove the barrel wobble that's been brought up. Otherwise, the solution would lie in the mount itself.

One way or the toher, this does not seem like an uncorrectable problem. The advantage of the 8" projectile over any 5" produced is pretty remarkable, and the 6 inch (155mm) is still only barely good enough for light targets. The 8inch seems to still be the lightest weapon we can have for effective NSFS and gunnery strikes.

[navydavesof]

Perhaps the barrel wobble is caused not by any inadequacy of the mount, but by the inadequate strength and stiffness of the barrel itself? This wouldn't bee the first time when large caliber weapons designed on too stringent a weight budget proved inaccurate because the light weight barrel flexed too much in the firing process.

That is an awefully good point. They were going to make mono-barrels for the production barrels of the Mk71. I wonder if the extra steel in the barrel replacing the liner would have compensated for such a lack in strength caused by the loose liner. Otherwise, I wonder if a heavier barrel, perhaps one from a Des Moines or such would have made for a better barrel.
From my learnings, contrary to earlier posts, the Mk71 was not just a single gun and loading mechanism installed inside a mount. The Mk71 had a significantly higher rate of fire, the barrel was designed for ERGM rounds, and the magazine subassembly was significantly different.
I believe the Mk71 mount offered such potential that it was one of the biggest losses the Navy made in gunnery, subjecting the service to 5" artillery.
Like it was said in US Cruisers, the Navy stepped away from real cruiser design, instead substituting the name "cruiser" in place of "frigate" or "large destroyer".
I think it's time to bring back the real cruiser, especially the heavy cruiser. The Des Moines-class offered so very much.
I look forward to the further posts, gentlemen!

[navydavesof]

This post is not accepting my posts when I quote! It's a conspiracy! I will try again.

With the barrel being too light, I wonder if that is the case. I then wonder if that was caused by the barrel bing a loose-liner barrel. The mono-barrels were what the Mk71 production barrels were going to be, and I wonder if the extra material in there would have strengthened the barrel enough to keep any fluctuations during actual firing.

Otherwise, what do you guys think about the utilization of the Mk71 mount? What kinds of improvements would you suggest to be made to the weapon itself that would make it a supportable system for all future DD and up ships?

[navydavesof]

Something else I found again is a NSFS support review published in the 1993. I read this a few years ago, but never could fine it again. Good olf globalsecurity.

http://www.globalsecurity.org/military/ ... 93/MCT.htm

What it talks about is my whole philosophy on NSFS, which is developing technology we have in order to fill the capability gap now. Since everyone is so against battleship reactivation, existing and technology that can be common should be explored heavily.
Battleships: There are no issues with the battleships. Boilers - no big deal. Big Guns - no big deal. That's what schools are for. Iowa's Turret2 - it was in the middle of being repaired when they were told to stop and ready for decommissioning; it's easily fixed. Propellant - make more. Life of the ships - they were made to serve the active fleet for 30-50 years with proper yard periods. These are not hard answers to the "problems" people perceive with the battleships. Here's the only real problem: We don't have enough of them to have 2 or 3 at sea at any one time. That makes them surge assets, and that is a problem, but the capability is there. Now, there is no capability at all.

Here, the Mk71 8"/55 caliber run dispersion rate is listed, and it's pretty problematic. 600m at 20nm. Wow. The laser guided rounds were within 2 meters...now we talking.
The Mk71 mount would be a further Mod with a 60 caliber monobarrel pushing the range of unguided 8-inch ammunition out to 22nm, and the mount would be able to fire the AP rounds of the heavy cruisers. I wonder if we're talking better accuracy because of the monobarrel or not. The 8-inch ERGM rounds would reach 100nm, a far more realilistic number thana 5" round going 120nm.

The 5-inch Dead-eye rounds were a little less accurate, but I bet modern laser seekers could get that down better and GPS would do the same.

Take a look at the report, and if you have gents, I'd love your input on it. I have to go swim and do a lot of working out for a few hours.

I will post a list of questions I am interested in hearing some of you answer afterward.

[Sean Hert]

The Army's new M982 Excalibur 155mm round has a CEP of 10m, and has shown in combat to hit with 4m over 90% of the time. Seems to me there's some technology ready for a naval application.

[SumGui]

I am a huge fan of 203mm due to weight on target, It really is that simple.

Projectile weight:
127mm - 69lb
155mm (Excalibur) - 106lb
203mm - 240-260lb.

The raw space availible also allows for more diversity in payload while still retaining effective hitting power.
One of the reasons ERGM was dropped was that even if they got past the G effects on the projectile at launch, they woul still end up delivering essentialy a 'coke can' to the target. Not much payload after all the effort.

8"/203mm would allow more space to absorb the G issues and still deliver a usefull load, and potential exists to use a 'collar' or sabot to put already developed 155mm shells out to a longer range.

[navydavesof]

I am a huge fan of 203mm due to weight on target, It really is that simple.

Projectile weight:
127mm - 69lb
155mm (Excalibur) - 106lb
203mm - 240-260lb.

The raw space availible also allows for more diversity in payload while still retaining effective hitting power.
One of the reasons ERGM was dropped was that even if they got past the G effects on the projectile at launch, they woul still end up delivering essentialy a 'coke can' to the target. Not much payload after all the effort.

8"/203mm would allow more space to absorb the G issues and still deliver a usefull load, and potential exists to use a 'collar' or sabot to put already developed 155mm shells out to a longer range.

Gui,

Your idea about the sabot is a really good one, man. It can be adapted wtih less than a 1" sabot on either side of the round.
I will be writing an article on NSFS for Naval Institute Press here pretty soon. I hope to get it done in a week and get it sent off. They take for EVER getting back to you.
Laser guided and GPS rounds are easy. It'd be so cool if we quit neglecting gunnery. We really thought we were going to get Des Moines back. It would have been great, and she would have been a real warship and the pride of the fleet. The Mk71 Mod1/2 MCLWG can produce quite a formitable capability to DDGs and possibly the CGs...

[navydavesof]

Over the past 2 years I have done a very deep level of research into the Mk71 MCLWG and its career. If you follow my work you know that I am a big advocate of the weapon system, and I have included it on nearly every WIF build I have begun. Here is some of the information I have found:

The Mk71 was/is a weapon system that was surrounded by conflicting reports. I was able to have extensive conversations with an FMC project manager on the Mk71, and my understanding is that a lot that made it out was incorrect information. From the USN, USMC, and FMC's points of view the Mk71 was a fantastic gun mount, and it was the future of naval gunnery. It was a little big and a little heavy, but it delivered ordnance that delivered in terms of kinetic energy and explosive yield was the equivalent of the impact of a Harpoon anti-ship cruise missile. The popular issues I know about are the same ones you have pointed out: accuracy and equivalency of ordnance with the 5" round. The issues were the barrel, propellant, projectiles, resulting range tables, and the seaborne platform USS Hull and its native GFC system.

Mk71page3.jpg

According to FMC the truth is that the mount fired groups of unguided rounds that were about 20% as large as 5" guns of any kind. The laser guided rounds impacted on or within 2 meters of their target. For the tests both at Dahlgren and on the USS Hull, the gun fired standard 8"/55caliber ammunition we had in stock that was developed for the 8"/55caliber guns of the WWII type heavy cruisers. Since the Mk71 carried an 8"/55caliber barrel one would imagine that it would perform the same way as other 8"/55caliber guns. However, the Mk71 was using a barrel with an elongated chamber designed to fit laser guided and ERG rounds (shortening the rifled length of the barrel), and the gun used a more energetic propellant to give it a 20nm range as opposed to the 18nm range of previous 8"/55caliber guns.
As you can imagine these variables influenced the performance of the projectiles designed for a lower muzzle velocity and rifle length. When firing at Dahlgren the gun performed spectacularly. It landed groups of standard munitions within 20m of each other. The rounds very commonly impacted directly on the targets. The Mk45 5" on the other hand has error as large as 600m at maximum range and can never, at any range, land groups as small as 20m. The Mk71 itself had different range tables than the WWII 8"/55caliber guns of the heavy cruisers.
The USS Hull, a Charles F. Adams-class DD was chosen to test the Mk71. While modifications were made to the Mk68 GFCS, the range tables for the WWII heavy cruiser 8"/55caliber guns were programmed into it instead of what was learned from Dahlgren. In addition to this error of incorrect range tables, the ship itself turned out to not be strong enough to support the weapon. While the bow was strengthened to take the recoil of the 8" gun, the bow still torque a little every time the gun fired. As you can imagine, even in the smallest degree, if the structure of the ship moves while the round is still in the barrel of the gun, the round will be thrown off course. That's exactly what happened. The other issue was that the projectiles were designed for a lower velocity propellant that did not throw them as far or as fast. The extra velocity also influenced their accuracy. According to FMC, as the USS Hull fired its rounds at San Clemente Island they landed in groups equal to that of Mk42 and Mk45 5"/54caliber guns: 600m in dispersion. Deflection was "significantly less" than that of a 5" gun. Even with these errors aboard the Hull, the laser guided rounds landed on target and were table to destroy massive portions of a target ship and prematurely sank the vessel during test and evaluation.
According to FMC, after evaluation, the prototype mount itself, the Mk71 Mod0 had a 20 or so changes FMC was going to make for the first production mount, the Mk71 ModX that was to be installed aboard a Spruance-class DD under construction. I believe it was going to be the USS Merrill. These included things like a 60 caliber barrel, stronger internals, and a new windshield for both USN and US Army 8" projectiles in storage.
Every ship of the Spruance-class DD and the first 5 Ticonderoga-class CGs were designed to fit the Mk71 in the bow. Every thing was on track to mount the gun and go into full production.

mk71-2small.jpg

FMC says the gun mount was suddenly and unexpectedly canceled by a Senator Proxmire in the late 70s. While it was canceled it was still of interest to both the USN and USMC.
In 1991 when the DDV study was underway the Mk71 was brought up again as a good fit for 20+ DDG-51s to take the place of the 16" guns of the 4 Iowa-class battleships.

Mk71fromDDV8inchstudy.jpg

So, in summation the Mk71 ModX 8"/60caliber gun was fully functional and ready to be installed aboard Spruance-class destroyers, the first Ticonderoga-class guided missile cruisers, and the Arleigh Burke-class guided missile destroyers. It seems that for political and certainly monetary reasons the Mk71 was discarded.
In addition to the historical reasons for dogging the 5" gun I know a number of SEALs who have called in 5" fire from DDG-51s, and they have nothing good to say about the 5" rounds. They say the 5" rounds...do not eliminate the enemy...at all...ever. All it does is delay the enemy's advance.
Since the onlyuseful form of the AGS is going ot be mounted aboard the DDG-1000s (the AGS-lite is still too big to be effective aboard DDGs) the Mk71 could quite very well take the place of the AGS in all future combatant builds and deliver superior firepower to either the Mk45 mod4 5" or the AGS.

Mk71page11.jpg

While it would be nice to have more R&D, no new precision guided ordnance is needed. The laser guided rounds can operate off GPS as well.

WNUS_8-55_mk71_Guided_pic.jpg

While it requires 6 more people than the AGS it can carry 300% more ordnance and can be fitted on all future DDGs and CGs that will come down the pipleline.

[Seasick]

The first 5 Ticonderoga CG were initially planned to have the Mk71 but it was decided to fit the 44 round Mk26 mod5 missile launcher forward in place of a 24 round Mk26 launcher. That ended their compatability with the Mk71 gun. The Virginia class CGN had a 24 round Mk26 mod0 launcher and was supposedly able to take the Mk71 in place of the 127mm/54 Mk45 mod0 gun. The Mk71 gun was canceled twice. Once by Carter, and once by Reagan. The Mk71 stayed canceled because of the supposed power of the Iowa's 16 inch rifles.

[navydavesof]

The Virginia class CGN had a 24 round Mk26 mod0 launcher and was supposedly able to take the Mk71 in place of the 127mm/54 Mk45 mod0 gun.

That's some fascinating stuff. That sounds like potential for a 1990s WIF model to me. A VLS and Mk71 modernzation...oh yeah.

The Mk71 gun was canceled twice. Once by Carter, and once by Reagan. The Mk71 stayed canceled because of the supposed power of the Iowa's 16 inch rifles.

Well, you know, we are all familiar with the limitations of gunnery in genearl, and there were excellent efforts to broaden the effectiveness of 16" gunnery that would prove fruitful if the battleships were brought back today. Sixteen-inch gunnery has always been peer with 500-750lb ordnance dropped from aircraft. The customers of naval gunfire (all military branches) have always been very pleased with 16" gunfire. When needing to replace the offensive and deterrent capabilities of an aircraft carrier, especially in the fiscally restricted USN budget, a battleship is a perfect ship. The capability lost by deactivating the George Washington in order to save $5 billion can be augmented by a battleship in its place at a $1 billion (max) reactivation and modernization cost. The battleships are remarkable platforms that are even today unchallenged in their effectiveness, longevity, survivability, and affect on the enemy or potential enemy.

While most of the allegations made against the battleships (worn machinery, inaccurate guns, cracked armor, level of difficulty in reacquiring the knowledge base, spare parts and gun barrels, etc, etc, etc...) are myths or exaggerations, this is the actual issue I see with the battleships: There are only 4 Iowa-class battleships available to the USN, and only 2 available for rapid reactivation today. As ordnance delivery platforms, they're great, and if they're available, they can be the best NSFS platforms one could ask for...but there can only 4 of them at any one time.

What can be done to solve the NSFS problem is the subject of this thread. The Mk71 is a fully developed platform that only needs to be reactivated and modernized to current radar cross section reduction needs (like the 1/350 pieces in my models). It sits silent at Dahlgren and is ready to go. The benefit the Mk71 has over 16" gunnery or the AGS is that it does not need a massive ship to be used like 16" or AGS. The 16" guns of course need enormous platforms due to their weight. AGS need enormous platforms due to their amazingly large size and power needs. The Mk71 is a Mk45 5" gun with a 20' base-ring and can fire 8" ammunition. When I approached BAE about 8" ammunition, it said it can step up 155mm (6.1") LRLAP rounds to 8" without a large R&D effort, and they would be significantly more capable. The Mk71 is a great gun, and it's what we should pursue for the DDG-51 restarts and every DDG and CG build after.

This way there are not just 3 DDG-1000s or 4 battleships available to provide effective NSFS. Every new DDG and CG would be able to do it.

The greatest value of the Mk71 is availability.

[cjwilks]

This is a cruiser concept I came up with based on the Des Moines class cruiser utilizing an updated Mk 71 gun mount.