Actually, the Marines used the 75mm armed gun. The 76mm was developed to combat other tanks. The PTO did not have a lot of enemy armor to defeat and the 75mm was a better infantry support weapon than the high-velocity 76mm.

USMC armor units are lower on the totem pole than US Army armor units. They got the left overs. Their most common tank was the M4A2 75mm followed by the M4A3 75mm as they became available. Additionally, high mobility on the battlefield was not a USMC tank requirement (no great vasts of open plains to maneuver on) so they mainly used the VVSS suspension system.

As far as flame tanks, USMC tank battalions consisted of 46 tanks (15 per company, 3 companies per battalion+1 for the battalion commander). One tank per company was a dozer tank. Later during the war, the battalions were given 9 flame tanks. These are the POA-CWS which stands for Pacific Ocean Area-Chemical Warfare System. The flame-armed Sherman used initially by the Marines was the M4A2 POS-CWS '75'. This type of tank fired the flame out the main gun. There were variants that fired flame from the bow gun mount and others that used the coaxial MG port. Only the USMC used the type of flame gun that fired out of the main gun.

1) Was the bow gun, the smaller gun barrell mounted on the mantle next to the 75mm ?

2) I was reading a book on Normandy, and there was a Tank battle being fought - They used an expression saying the Tanks were in a " HULL"S DOWN POSITION ".
Can you please tell me what that phrase means ?

Not to cut in on you Rob, but isn't that used to describe when keeping the tanks from rising on a crest and exposing it's "belly"???