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The M-3 was too small to make a useful APC. See the Recce modifications with turret removed. needed 3 vehicles to transport a single squad isn't going to work. The other thing about Americans building some of these other versions is that they had halftracks out the wazoo.
Many of the functions could be done by halftrack conversions and done better. Half tracks provided the SP AA mounts, SP mortar mounts, SP 75 howitzer mounts, SP 105 howitzer and 75mm AT gun mounts.
In most cases they gave the guns crews more room to work and carried more ammo.
The Germans did a lot of those conversions because they had to. Lack of production capacity+ short development time. No or little MK III/IV production capacity to spare. When you get to the 105 Howitzers (Wespe) the use of too small a chassis starts to show. It carried 32 rounds of ammunition. Four every 4 gun armed vehicles there was a 5th without a gun that acted as an ammo carrier and spare chassis that a gun could be swapped into. The American M7 carried 69 rounds.
If you are talking about a "what if" in which the Americans had some bizarre reason only the M3 light chassis to work with then some of the vehicles make sense. With the M3/M4 chassis and the halftrack chassis available they don't.
im not convinced that light tanks are a waste, mostly because the concept continued after the war. but i would concede its changed considerably since the war. The one that comes to mind are the m-41 Bulldogs and AMX-13s at the heavy end of the spectrum. at the light end you have the LAV-25, and the russian BTR90 and the various turretted versions of the m-113 such as the ARVN ACAV and the australian turetted variant of this concept . The brits developed the scorpian striker and spartans, along with a wide range of other light tanks.
On a related issue, too bad the 105 M3 was not tried at US halftracks. While offering a much heavier punch than 75mm, it was substantially less powerful (lower MV) than the M2, so the recoil wouldn't be such an issue?
Or just bolt the muzzle brake on M2, for same (better?) effect.
And, how about this combo: Vickers light tank Mk. VI + 18pdr, later + 25pdr. Another reliable vehicle married with reliable gun.
Before you start laughing, Germans were using those hulls as platforms for 10,5cm M.1916 howitzers, and were satisfied according to Jentz.
From wiki "The production started in February 1943 and continued until May 1944; an additional bunch was produced in April-June 1945"
By the time they actually had M-3 howitzers they had M7 self propelled howitzers.
And the half track 75mm howitzers were fading from service.
18pdr was on the way out in the mid 30s.
Germans were satisfied with what? mobility in comparison to 4-6 half starved horses?
A top heavy vehicle with limited ammo capacity, limited gun crew with limited space to work leading to a low rate of fire and, unless a fair amount of work was done, rather limited traverse of the gun 4 degrees total or 4 degrees each side of the center line? A Wespe had 34 degrees of traverse and an M7 had 45 degrees (more to the right than to the left but still?
4 degrees is roughly a width of 667 yds at 10,000yds. If the target is outside of that "pie slice" the vehicle has to be shifted to bring the target into the covered arc rather than just traversing the gun.
Perhaps I wasn't clear. that quote is for the production of the M3 105 howitzer. By the time you have any numbers (more than a couple dozen) and can actually move them from the factory to a combat front it is mid 1943.
With the Sexton already in progress (prototype completed in June 1942) perhaps we should take another look at the real history:
British did request 5500 M7s, but when?
90 are Shipped to the British in time to be used at El alimein. A little early for the M3 howtizer without a time machine no matter what chassis it is on.
British are so short of SP guns that by Oct of 1944 they start converting 102 M7s to Kangaroo APCs.
British had supply problems with M7s because the 105 howitzer was not a standard British round. Solution is to give them more tubes that use non-standard ammo?
Same consideration goes for giving any of these things to the Russians. They never got ANY 105 howitzers so a special supply line would have to be set up. And special is the right word. A single 105 howitzer barrel was good for at least 5000 rounds before it needed replacement. That is about 82.5 tons of projectiles not including cartridge cases or propellant.
SP howitzers were needed on pacific atolls why? It must have been a real problem moving those towed guns 5 miles or less.
You brought up Kwajalein, what did SP guns really bring to the battle?
File:Kwajalein Atoll;p12(map).gif - Wikipedia, the free encyclopedia
The Russians weren't particularly interested in American/British field artillery. I don't know why SP versions would have been greeted with great joy.
To make really good use of SP guns instead of just having a tracked gun you need the command and control to go with it. A better radio net (field phones can't keep up with gun movement) good maps and good survey teams. If the new target is really 5 miles away instead of 4 1/2 your first ranging shot may just land on your own forward observer.
The British knew what they wanted and MK VI chassis wasn't it.
BTW, I am not sure the British ever got ANY 75mm howitzers on half tracks, they did get 75mm guns on half tracks.