Yet 3" and 3.7" CSBy later in the war, with 75mm HE in use in tank guns, then they could support each other and their infantry with HE fire but it is a rule of thumb that a 75mm shell is the minimum needed for effective HE fire. Hence the 75mm on the Char B.
diameter was good, the propelling charge, not so much.
3.7" was 94mm, with a 20 pound shell. Its 1000fps MV, not much better than some mortars. US 75mm Pack Howitzer had an 18 pound HE shell, with 1250fps velocity.
Well liked with the M8 GMC and LVT(A)4