I apologize if I am covering old ground here.......


I was on another board a while back and it was said that when the US Army switched from the M1IP to the M1A1 there were many - with good reason - who wanted to stay with the 105mm gun instead of upguning to the 120mm gun.

What was the 'good reason' for wanting to stay with the 105?

Does it offer any significant advantages? Back then? How about still today?

I figure there were logistics reasons that favored the 105 if only because they had been around for so long and there was already such a good stockpile but that applies to any new system. The 105 is also physically smaller.

I have heard that the 105 is more accurate at longer range due to the rifling, but I have no idea if that's true or not.

My understanding is that the 105 is more versatile in it's ammunition types, but I don't know if that is a matter of it's nature or a matter of a lack of developement of the 120. We just recently got a cannister round for the 120, and I don't see a reason it couldn't have been done years ago. I also understand that the 120mm HE round is less powerful than the 105mm due to the fin vs spin stabilization issue, but the 120mm HEAT round is more powerful partially for the same reason. Is that at all correct?

Other than that, are their any advantages to the 105 mm?

If there were an M1A2 and a Stryker MGS together, is the Stryker better off in taking out a target than the M1 in any cases? If so, which ones?


Also, how much do nations still rely on tanks with the 105mm gun today? How effective would they be?



-K

I don't know of any good reasons or anybody that thought the switch a bad idea. I certainly didn't.

Perhaps the M724 was marginally more accurate than the M865 but being training rounds the comparison is irrelevant. Of course the M1A1 carried far fewer rounds than the M1 and M60s but that was offset by greater lethality round to round. As far as accuracy with service ammunition I found the M829 very accurate, its dispersion tolerance for service ammunition no greater than equivalent 105mm rounds. Moreover because the 120mm isn't rifled tube life is inherently greater.

With regards to the Danish Army scrapping its Leopard 1A5-DK and sending the Leopard 2 to Afghanistan - switching from a 105mm armed tank to a 120mm armed one - it has been argued that the 105mm was the preferable weapon due to ammunition issues. Denmark does not have 120mm HE and there seems to have been some affection for the 105mm HESH for use against the types of "soft" targets that most of the fire is directed at in Afghanistan and previously in Bosnia.
HESH, of course, doesn't work well with a smooth-bore gun and I'd assume that there might be issues with HE as well, since fin-stabilization requires some considerable velocity for good accuracy which might require stronger HE shells with less explosive. But that is guesswork on my part.

cbo

Russian 122-mm artillery and 125-mm tank smoothbore HE rounds are probably a fair comparison:

122mm 3OF56 (modern round for D-30) 21.8 kg projectile, 690 m/s mv, 4.1 kg HE content.
122mm OF-471N (WW2 ammo for A-19 gun): 25 kg projectile, 800 m/s mv, 3.8 kg HE content.
125mm OF-19: 23 kg projectile, 850 m/s mv, 3.15 kg HE content.

So you seem to lose about 20-25% HE content by going for smoothbore instead of rifled HE, my guess is most of that probably comes from the fin assembly rather than need for a stronger shell. Then again, OF-19 might well be the better choice to shoot at say an IFV or a strong concrete structure.

Logistics, for sure. Many 105 mm rounds in stock. And less 120 mm rounds = less potential kills.

National (or developer) pride might also count. Idea of buying German tank instead of US one (nevermind with UK roots) was bad, not so good was also getting German gun.

Also, US put much money into 105 mm APFSDS program. 105 mm DU monobloc long rod penetrators were comparable with first 120 mm APFSDSs. 120 mm got potential, 105 mm was good enough (as it was thought in this times) and "on hand".

Back in the Cold War the United States Army many felt that 120mm ammunition was not mature enough. It seems the Germans originally had some problems with the combustible casings. The Army was still very cautious after the failures of the 152mm gun/missile launcher. Plus 105mm APFSDS like the M833 was still very capable, and there was plenty of 105mm ammunition stockpiled.

At the moment the 105mm gun also has a wider array of anti-personnel ammunition. With the 105mm you have WP, HE, HESH, HEAT, APERS (flechette) and Canister shells to use against enemy infantry. While for the 120mm gun, the Army only has HEAT-MP, Canister, and a pure HE shell for demolition.

Right now I think all of our main battle tanks, as well as the FCS MCS should have 120mm guns, but we should get some different types of ammunition. Having a few lighter vehicles like the Stryker MGS armed with a 105mm gun is a good choice however.

Only advantage I can think of is 55 stowed rounds on board.

I remember reading US tankers in South Korea were particularly unhappy with reduction of number of stowed kills, arguing (quite reasonably) that NK didn't have anything that would require 120mm anyway...

The Soviets certainly did! Reading "King of the Battlefield" I couldn`t believe there was so much lack of knowledge on real Soviet protection developments. of course 105mm was enough for what it was believe the menace was, but woefully short with current knowledge

Fortunately the 120mm bunch won.

Ammunition quantity importance is easily underestimated.

Tanker reports from wartime stress this very much.

Examples; fights for single fortified villages required ammunition resupply for 90mm M48's, the Russians (which actually have an effective HE-frag munition) used tank rotations in Chechnya village combat to cope with the ammunition resupply challenge.

The German tank crews of late WW2 had rarely stowage problems, though. Their ammunition supply was so small that they could rarely fill the storage bins anyway.

OTOH there are reports that many tanks in Chechnya fought with ammo just in autoloader to have less chance of brewing up, so I can imagine that in an intense inf support the tank may go through the 22 autoloader shells pretty quickly.

There is no accounting for taste and nostalgia, especially among old tankers. At the moment the USMC was finally acquiring the M1A1 series tank, some tanker colonels on the verge of retirement were telling our senior tanker, Gen. Martin Steele, that "we never should have given up the M-48s." The variety of ammo and numbers of stowed rounds were hard to give up, and many tankers had already viewed the demise of the 90mm rounds with incredulity & disbelief.

The USMC toyed during 1988-90 with retaining the 105mm and the arduously accumulated ammo stocks we had by going to the super-M60 offered by Teledyne, etc., but in the end the realities of protection, ammo performance and suspicions about US Army continuing support for the M68 series cannon tipped the balance.

Would it be possible to mount as 105 into M1A2 easily? Might be a good "convertible" then

No reason it can't be done, afterall, the M1A1/2s are merely upgunned M1s. OTOH, as Ken pointed out, if there is no expected support for the M68 series of cannon....

But if the spares system is what it usually is I would think the USMC would be well supplied.

I would think the US Army will continue to support the M-68 - didn't they just pull old cannons out of storage to put on the Stryker MGS? I figure they will be around for a while yet unless they find a way to put a 120 in the Stryker.



-K

I'm not sure, but I heard that the talk about old cannons to be used in MGS became a victim of requirement creep and the MGS uses new guns.

If you are in a combat zone you may be well supplied, otherwise you float your bad part and hope another one becomes available within the next 6 months. Thankfully DLA would not have any cog over any M68 parts.

Interesting. I hadn't heard of this.

Anyone know for sure?





-K

The USMC LAV-AG project (KIA 1990) was using the XM-35 short-recoil 105mm gun, capable of using all M68 ammo; I would assume the LAV III variant went the same way, but I've not followed it.

Not easily but it can be done. Its not just the gun tube and breech. Its also the entire mantle, mount, elevation mech. parts of the FCS, "software" (which is really hardware), and all of the ammo racks. These and their mountings were not completely interchangeable between M1 and M1A1+.