M10 Tank Destroyer and M4 Sherman

Some of the blame must fall on the Join Combined Chiefs of Staff - and the British who opposed a 1943 D Day. It was difficult for the ordnance board and armaments industry to plan the right mix of armaments and developments in 1942 for weapons which might be available in 1944 for a war which might be over any time from 1943-46. A decision to produce Pershings, which might not be available in 1944 would have been at the expense of M4s which would not have been available in 1943 if the Second Front was to be launched then. (Of course had the second front have been launched in 1943 and failed, then Pershings might have been needed for a Ww2 lasting until 1948-50

The further issue was shipping space. Accordign to Ian Hogg, the decision not to proceed with US heavy tanks was because one heavy tank took up shippoing space for three mediums. Given that shipping was the bottleneck preventing deployment of the US Army it made a huge amount of sense to base the US Army on a medium tank fleet. The top trumps obsession with the "best tank" misses the real logistic and financial concerns which made a difference. For all the drooling over the performance of the heaviest tanks the facts are that the US had a winning strategy. Its army had a mix of tanks and TDs which could taken on and defeat the Germans when they met them from Mortain to the Bulge and were able to deploy enough forces to take the lead in the land campaign which ended WW2.

 

The Pershing was opposed by a number of powers (including the Engineerind school). The best option would probably have been a Sherman with a 90mm turret. I don't see Pershing's making it to Normandy with or without NcNairs support.

Well they did develop a turret armed with a 90mm gun that would fit on a Sherman. Actually I believe the Pershing turret would. That would have meant that you could still use the same bridging equipment and it could have been worked into the production stream easier.

 

That shipping/landing craft thing was a massive factor, too often brushed aside by those in favour of Pershing-was-possible-earlier nonsense like Cooper.
The sheer effort put into Supplying landing craft for Anzio & Normandy could fill a book in it's own right - a desperate situation involving an utterly basic requirement for mainland assault.
Tell them at Southwick House in 43-44; 'Sorry, chaps, we've just made all your landing craft obsolete for the amount of tanks you want to get ashore'... See how that would have gone down...

More Pershing-related Ramblings here:
Why didn't the US standardize the T23E3?

 

Not just the landing craft either. The Sherman was right at the limit of what the standard class crane on freighters could handle (I'm not sure if a 90mm armed one would have been over or not). This means Pershings could only be loaded and unloaded on most vessels in ports were a heavier duty crane was available. I'm pretty sure the Mulberries didn't qualify, I'm not sure how many of the ports captured in the first couple months had cranes of that class operational either.

 

Absolutely. There availability of merchant shipping to carry troops and supplies across the oceans was a major constraint on allied operations, made worse by the Germans U boat campaign which sank a huge tonnage until mid 1943. The argument that shipping oculd be saved by re-opening the Mediterranean route was a major factor in . the allied decision to invade Sicily. The shortage of specialized Landing Ships Tank constrained the scale and number of assaults that could be launched. Until January 1944 Operation overlord was doomed to be launched with a feeble assault force of three divisions because of the shortage of assult shipping. It took the political clout of Eisenhower.and a lot of fast work by ship builders and the Navies to build enough landing craft and train the crews to launch the extra two diviisons into Normandy. This could not have been achieved until the U Boat campaign had been won as the yards that built LSTs were the same that built corvettes.

 

The people who wanted Pershings to fight in Normandy did not consider the problem of invasion planning. Overlord was planed through '42-'44; LST and M4 tank were designed and built around '40-late '42. According to Hunnicut, M4 tanks were being loaded into LSTs earmarked for Overlord even as the US Army was struggling to prevail against the Wehrmacht in North Africa. The stockpiling of equipment and invasion schedule simply could not accommodate the introduction of vaporware.

 

There is an additional problem. The lesson of WWI is a war economy must centralize ruthlessly and unnecessary expenditure of time avoided at all costs. Having a complete suite of mass produced weapons of adequate quality allowed applying overwhelming force in combined arms formations. That was the premise of US strategy. The US mobilization during WWI almost failed to achieve this, and the generals who fought that war as staff officers and regimental commanders were not going to mess with any repeat of the last war's failures.

Also, the quality of tanks would have made very little difference in close combat that prevailed in the bocage. Brit 21st AG's operational research stated 2/3 of all their tank casualties were lost to flank or rear shots. A significant minority of tanks were knocked out at ranges under 400 meters. You can't build a tank proof against the Panther's 75mm L/70 or Tiger's 88mm L/56 gunfire from those aspects and at those ranges.

 

The tendency was to weld OHP when they could.