The Largest APCR Projectile on a Tank Gun: T35E1 HVAP

This was the largest APCR projectile to be developed for a tank gun in WWII. Designated as Shot, H.V.A.P., 155MM, T35E1, or just simply called as T35E1
The 155 mm T35E1 HVAP, and 90 mm M304 for scale.
Grown out of the concern from encountering enemy heavily armored tanks, the U.S. Army Ground Forces was pressed to develop a necessary anti-tank munition for their latest heavy tank in development, the T29 and T30. These tanks were intended to support allied forces with combined heavy armor and heavy firepower to defeat the most well-fortified enemy positions with different roles. The T29 would be used to combat other tanks with its 105 mm gun, and the T30 would be relegated for anti-fortification with its 155 mm gun. Leaving the T29 aside since it was was built to confront hostile armor anyway, the T30 was stuck with no self-defense munition to hit back should it come across opponents like King Tiger or Jagdtiger.