MK 71 Lightweight 8" gun.

[cjwilks]

The attachments are awaiting approval.

 

[sferrin]

See attached.

 

[TomS]

Oh, that's nice. Thank you for digging it up.

 

[cjwilks]

How long does it take for attachments to be approved? I put some on 5 days ago, and they still show waiting approval!

 

[Pioneer]

See attached.

A 60 calibre barrel for increased range

So how long was the trial Mk71's barrel then?

Regards
Pioneer

 

[sferrin]

From NAVWEAPS:

"The gun barrel for the Mark 71 was the Mark 28 Mod 1, a 55 caliber two-piece loose liner barrel. The production gun mount was to have used a one piece monobloc barrel designated as the Mark32. "

 

[SpudmanWP]

I don't understand why I have never seen a naval gun with a muzzle break. This should help reduce stress & recoil through the ship.

 

[TomS]

I don't understand why I have never seen a naval gun with a muzzle break. This should help reduce stress & recoil through the ship.

There are some -- the OTO Melara 76mm has one, as do some guns in the OTO 127mm family, for example.

 

[Yellow Palace]

I don't understand why I have never seen a naval gun with a muzzle break. This should help reduce stress & recoil through the ship.

A muzzle brake also significantly increases blast overpressure in the surrounding area. On ground vehicles this isn't such an issue, provided that the surrounding area doesn't have too many people around, because dirt is pretty hard to break and nobody really cares if you do break it. On ships, you have to provide additional structure to deal with the overpressure. In general, it's preferable to make the gun mount strong enough to handle the full recoil of the weapon, rather than have to beef up quite a bit of the upper decks and superstructure. Though there are always exceptions to any rule of thumb.

 

[isayyo2]

NPS thesis on MK71 ammunition :DTIC

 

[1635yankee]

Thanks heaps for this info Abraham Gubler
These look very impressive proposals/programs
Are there any drawings/artist impressions to go with these ? ??? ;D

One thing that I have never completely understood is the US Navy's apparent reluctance to consider, let alone field a navalized variant of the army's MLRS system!
Ok some people would say that to use them would bring US Amphibious units into harms way!
Some would say that the loading/reloading process is unacceptable on a ship!
Its strange - but as far as multiple rockets launchers on Western/NATO ships go in the amphibious support fire role, I think only the Italian navy utilize them aboard there ships(??)

Regards
Pioneer

I know this is a decade after the post, but the USN did consider the MLRS for naval application. The problem, I read, is that the MLRS's rockets exhaust gases were very corrosive. While a less corrosive fuel-oxidizer grain could have been developed, this would have been non-trivial and could have resulted in a decrease in performance.

 

[1635yankee]

A Spruance Mk71 study can be found here: https://apps.dtic.mil/sti/pdfs/ADA100430.pdf

 

[isayyo2]

Naval Gunfire Support of Amphibious Operations: Past, Present, and Future (1977)
By Donald M. Weller, Major General USMC (Ret.)

https://apps.dtic.mil/sti/tr/pdf/ADA051873.pdf

A good read if you have ~20 minute to spare, goes into detail on the 8" MCLWG and its advantages over existing 5" guns on destroyers. The 8" guns have 1.5-2x the range and 5x the lethality over the 5"/54. However future range requirements to strike rear-echelon forces and support heliborne assaults needed a weapon to hit out to 100km - about the same range AGS with LRLAP was supposed to provide...

 

[Scott Kenny]

Naval Gunfire Support of Amphibious Operations: Past, Present, and Future (1977)
By Donald M. Weller, Major General USMC (Ret.)

https://apps.dtic.mil/sti/tr/pdf/ADA051873.pdf

A good read if you have ~20 minute to spare, goes into detail on the 8" MCLWG and its advantages over existing 5" guns on destroyers. The 8" guns have 1.5-2x the range and 5x the lethality over the 5"/54. However future range requirements to strike rear-echelon forces and support heliborne assaults needed a weapon to hit out to 100km - about the same range AGS with LRLAP was supposed to provide...

View attachment 731896
View attachment 731897

Where did the General get 40k yards out of the 8"Mk71? USS Hull trials only gave it 32k...

My evil thought process would be taking the 8" bore and a subcaliber projectile... I mean, the standard 8" HE shell weighed 260lbs/120kg, while the very long (14.5 calibers, 224cm) 155mm LRLAP was 225lbs/102kg. Using a ~44"/112cm long projectile weighing about 110lbs/50kg, you should be able to punt that downrange at over 4000fps/1200m/s.

And since a 44"/112cm long projectile is the same length as the 8" HE, it should be compatible with the existing shell handling equipment. Also, that should still allow the use of full caliber 8" shells as well if you need to throw large booms at something.

 

[isayyo2]

Where did the General get 40k yards out of the 8"Mk71? USS Hull trials only gave it 32k...

I'll quote what the General wrote on Page 7:

On the other hand, the 8"/55 MCLWG and an improved projectile with a range of over 40,000 yards could have satisfied this requirement.

Now what exactly entails in "improved projectile" is not stated directly by this paper; whether it's a Base Bleed or Rocket Assisted round. Laser and IR guided rounds are mentioned however to bypass any dispersion concerns over long-range, while bomblet ICM rounds were also to be developed to shred through soft target over a wide area.

 

[Firefinder]

Where did the General get 40k yards out of the 8"Mk71? USS Hull trials only gave it 32k...

My evil thought process would be taking the 8" bore and a subcaliber projectile... I mean, the standard 8" HE shell weighed 260lbs/120kg, while the very long (14.5 calibers, 224cm) 155mm LRLAP was 225lbs/102kg. Using a ~44"/112cm long projectile weighing about 110lbs/50kg, you should be able to punt that downrange at over 4000fps/1200m/s.

And since a 44"/112cm long projectile is the same length as the 8" HE, it should be compatible with the existing shell handling equipment. Also, that should still allow the use of full caliber 8" shells as well if you need to throw large booms at something.

I'll quote what the General wrote on Page 7:

On the other hand, the 8"/55 MCLWG and an improved projectile with a range of over 40,000 yards could have satisfied this requirement.

Now what exactly entails in "improved projectile" is not stated directly by this paper; whether it's a Base Bleed or Rocket Assisted round. Laser and IR guided rounds are mentioned however to bypass any dispersion concerns over long-range, while bomblet ICM rounds were also to be developed to shred through soft target over a wide area.

Needs to be point out that tge Army and Navy 8 inch projectiles were interchangeable.

With tge Army getting 32km from their M110 L25 howitzers with Rap shells. Or bout 35k yards.

Putting tge Same shell in the Mk71 which is bout 30 calibers longer you would easily get 40k yards.

Then you need to factor in the Navy own long Range shells.

Like the Gunfighter Shell the USS St Paul used with the same gun type, an 8"L55, to blap a North Vietnamese ammo dump out to 70,000 yards. They only made bout a hunderd or so of those shells so the Hull never got any, but the Mk71 mount was design with those shells in mind with wooden mark ups being used to ensure clearances

Also I remember reading that the Hull trials limited the max elevation of the gun to bout 41 degrees instead of the full 65 which would cut a the range down a bit, due that being the same angles of the heavy cruisers guns and as such could use the ballastic calculations. Which does much up with the range figures given. Basically a copy paste of the heavy cruisers figures.

 

[Scott Kenny]

Needs to be point out that tge Army and Navy 8 inch projectiles were interchangeable.

With tge Army getting 32km from their M110 L25 howitzers with Rap shells. Or bout 35k yards.

Putting tge Same shell in the Mk71 which is bout 30 calibers longer you would easily get 40k yards.

Okay, hadn't considered that. Should have, but I think I'm too used to thinking in terms of Army and Naval guns not being compatible.

Then you need to factor in the Navy own long Range shells.

Like the Gunfighter Shell the USS St Paul used with the same gun type, an 8"L55, to blap a North Vietnamese ammo dump out to 70,000 yards. They only made bout a hunderd or so of those shells so the Hull never got any, but the Mk71 mount was design with those shells in mind with wooden mark ups being used to ensure clearances

Oh?

*navweaps dive*

In the late 1960s the "Gunfighter" program at Indian Head Naval Ordnance Station developed Long Range Bombardment Ammunition (LRBA) projectiles. These were Arrow Shells with a body diameter of 4.125" (10.4 cm) and a fin diameter of 5.0" (12.7 cm) which were sized to be fired from 8" (20.3 cm) guns by using a sabot and obturator system. Tests with these in 1968 showed maximum ranges of 72,000 yards (66,000 m). The burster in these shells was PBX-w-106, a castable explosive. Sabot weighed 17.6 lbs. (8.0 kg) and was discarded as the projectile left the muzzle. After a test firing off Okinawa of three inert-loaded shells, USS St. Paul (CA-73) in 1970 conducted a two day bombardment mission against Viet Cong positions at ranges up to 70,000 yards (64,000 m). At the time, St. Paul was the only 8" gunned cruiser still in active service.

Shell overall was ~110lbs/50kg and 54"/137cm long, MV of ~4000fps/1200m/s. Interesting...


Image from NavWeaps, courtesy of Matthew Rodchenko

Smaller diameter than I expected, but definitely the kind of thing I had in mind! And we could definitely get a better sabot today, borrowing tech from the tanks.

 

[isayyo2]

Video on the US Navy BuOrd's 1970s Gun Improvement Program:

Mainly concerns the 5"/54 Mark 42 Mod 10, improved fire control by adding new systems to the Mk 68 fire control system, improved types of ammunition, including laser-guided, and briefly mentions a proposed follow-on to the 8-inch Mk 71:

View: https://youtu.be/Sd9lNJFF0uo?feature=shared

Highlighting the conceptualized follow-on to the Mk 71, it was to be:
- 35% smaller
- 70% more reliable
- An expected 3000 Mean Rounds Between Failures rate, 10x the Mk 42 and 3x the Mk 45 failure rate

Screenshots of the mount from the video below, also shown is an A-6 with presumably TRAM guiding a PAVEWAY shell onto an enemy ship with a claimed 50 nmi range.

 

[Scott Kenny]

Highlighting the conceptualized follow-on to the Mk 71, it was to be:
- 35% smaller
- 70% more reliable
- An expected 3000 Mean Rounds Between Failures rate, 10x the Mk 42 and 3x the Mk 45 failure rate

Screenshots of the mount from the video below, also shown is an A-6 with presumably TRAM guiding a PAVEWAY shell onto an enemy ship with a claimed 50 nmi range.

Going from a built-up gun to monoblock construction would probably account for most of the smaller size. While the gun would still be bigger than the Army 203mm (~8-10 tons, the M115 is 31klbs on the mount), either from a cooling jacket or heavier construction, it wouldn't be a 20 ton monstrosity like the built-up gun was even with the 60cal barrel.

What do you think they meant by "35% smaller"? ~65 ton turret? Or actually .65x every dimension, for a turret that is .28 the volume?

That MRBF goal looks very challenging to meet. IIRC, the Mk71 turret was heavily based on the Mk45 internals, just scaled up from 127mm to 203mm projectiles. In general with firearms, scaling a weapon up doesn't work as well as scaling down. But I still think that getting to the Mk45 failure rate of ~1000MRBF would be not-trivial but easy. Getting to a 3000MRBF is going to take a lot of work.

 

[uk 75]

Unless you have air superiority putting a Spruance sized warship close to a shoreline seems a bit risky. I wonder if this didnt help kill the idea off?

 

[Firefinder]

Unless you have air superiority putting a Spruance sized warship close to a shoreline seems a bit risky. I wonder if this didnt help kill the idea off?

to be fair the USN has made sure to have two CVs types covering the potential landing zone since WW2. In addition to any Amphibious types in the operation.

So at worse you looking at Air Parity.

And thats not including the ADA ships guarding the AO.

Cause Air Attack is one of the best way to delay if not stop a landing. With Delay being the more likely goal so the ground force can have time to set up lines and like to repell the landing.

So unless you doing mudhut stomping a Spraunce with Mk71 will have air protection nearby.