The LVTA4 mounts the 75mm Howitzer M3. This is a LOW velocity gun that only fires HE rounds.
The 37mm manned ack you are talking about is a high velocity gun, and its rounds are still both AP/HE in the game; and they haven't been changed over to pure HE like the Ostwinds were (at least from what I can tell).
Bottom line: HE shells are unlikely to penetrate tank armor unless you are at close range and firing on the sides of the tank. Even then, the penetration is more than likely the result of the force of the explosion on the armor itself.
As for the 37mm AAA's AT capabilities against armor, HT hasn't commented on it when it has been brought up before (that I know of, anyhow). I'm still hoping to see AT guns taking the place of the manned ack as tank defense for fields sometime in the future.
