I was just admiring one of Guntrucks models, "Babs" an AFV M-10, and a question came to mind. Can anyone tell me why US tank destroyers such as M10 and M36 were designed with an open vice closed top? Did it have to do with ease of loading the gun or was there some other reason?
Thanks,
Cob

So as not to confuse them with Tanks? But the M-10 & 36 were essentially tanks. So I am not really sure why the braintrust of American military design decided to take AFVs with better guns and give them weak armor, but AFV's with better armor weaker guns.

They wanted to give the tank destroyers better visibility. Also less weight to be faster and have better mobility.

Tanks are an expensive piece of equipment that seldom lasts long in combat. They were used for both offence and defence.
A tank destroyer is basically the same thing without all the protection of added armor. This offers two advantages: first, it's cheaper, and second, there's more room in an open turret. With more room, you can fit in a bigger gun. The bigger guns were too big to fit in the current run of tank's turrets. Thus, for the same amount of money, you can have more tank destroyers with bigger guns. Quite literally, more bang for the buck. Because they were lighter in weight because of less armor they were faster!
TD's were used for hit and run tactics. Their motto or mission was "SEEK, STRIKE AND DESTROY"

The Tank Destroyer Board, thought it best for an open topped turret, because it allowed for a full 360 degree view of the battlefield surrounding's to scope out enemy tanks & infantry. Although, there were some unit's who rigged their own armor enclosures, and other overhead protection with - wood - log's & sandbag's. There were also some M36B2's with an armored overhead hatch kit ( though few were seen in photo's ). As for the thin armor, this made for a faster TD for the U.S. - which they used for
"shoot and scoot " battlefield tactic's, and this was very effective on German tanks kill's. The M18 was THE fastest fully tracked vehicle of W.W.II, with a speed of 50 MPH.
So the U.S. basically substituted armor for speed, and it worked well. The Germans had bigger gun's and much better armor, but this made for their tanks & TD's getting bogged down alot, and especially made them to heavy and incapable of crossing alot of bridges.
Where as the U.S. TD's would have no problem, and get right over them. The light weight
because of the thin armor also made it quick for the U.S. TD's to get out of harms way very fast. But if they were hit by a Pz. IV or better, or a German Anti-Tank Gun, it was a total loss.
And the open toped turret, though proved great for visibility, was also a liability from snipers, grenades, etc. etc.
One thing for sure - the U.S. TD's made a big difference in the war and were able to go up against and defeat Panther's, Tiger's and a few King Tiger's.

- ralph