(see description below) Courtesy of Bill Ives 5" 54 caliber anti aircraft projectile with a VT fuze (the fuze sends out a radar pulse, and when it receives a strong enough return signal that indicates the target is within range of the shell burst it detonates) 4" 50 caliber "common", actually an armor piercing projectile, has a base fuze to allow penetration of the projectile before it explodes. 4" 50 caliber high capacity projectile. high capacity means it has a thinner wall than an ordinary high explosive round so they could stuff more explosives inside. I am not familiar with this particular fuze, most likely it is a combo time and impact fuze. 5" 38 caliber anti aircraft projectile with an infrared fuze. This fuze would pick up the heat from the plane engines and detonate when the heat level indicated the target was within burst range.