The M1E1 cupola design used a G305 cupola riser with 9 non-removable vision blocks installed (some versions had 7 with the 2 rear blocks deleted) between the turret roof and the cupola. It also came with a new bulged hatch cover to provide the tank commander with more headroom and allowed him to reload the weapon while remaining under armor protection. A major drawback of both these cupolas was their inability to mount either daylight or infrared vision devices. The receiver of the M2HB took up a great deal of space in the already cramped cupola's interior. Also due to restraints in the cupola, smaller 50 round ammunition boxes were used. Development of its eventual replacement, the T9/M19 cupola of the XM60 tank was continued into and some M19 cupolas were retro-fitted to M48A5s to allow for the use of IR and daylight periscopes by the commander.