The Sperry ball turret, meant for ventral defense needs on aircraft, was used on both the B-17 Flying Fortress and the B-24 Liberator as well as the Navy's Liberator, the PB4Y. The Sperry ball turret was very small in order to reduce drag, and was typically operated by the shortest man of the crew. To enter the turret, the turret was moved until the guns were pointed straight down.
The gunner placed his feet in the heel rests and then crouched down into a fetal position. He would then put on a safety strap, close and lock the turret door.
The gunner sat in the turret with his back and head against the rear wall, his hips at the bottom, and his legs held in mid-air by two footrests on the front wall.
This left him positioned with his eyes roughly level with the pair of light-barrel Browning AN/M2 .50 caliber machine guns which extended through the entire turret, and located to either side of the gunner.
The cocking handles were located too close to the gunner to be operated easily, so a cable was attached to the handle through pulleys to a handle near the front of the turret. Small ammo boxes rested on the top of the turret and the remaining ammo belts were stowed in the already cramped turret by means of an elaborate feed chute system. A reflector sight was hung from the top of the turret, positioned roughly between the gunners feet.
The turret was directed by two hand control grips with firing buttons similar to a one-button joy stick. Hydraulics normally powered elevation and azimuth. Hand cranks were available for backup. The left foot was used to control the reflector sight range reticle. The right foot operated a push to talk intercom switch.
On the B-17 the turret was close to the ground, but had enough clearance for takeoff and landing. However, the gunner did not enter the turret until well into the air, in case of landing gear failure. In the case of the B-24 the Liberator's tricycle landing gear design required that the turret mount be made upwardly retractable into the lower fuselage while the aircraft was on the ground, since with the ball turret deployed for operation, the shell of the turret would be too close to the ground. For both aircraft types, there was no room inside for a parachute, which was left in the cabin above the turret. A few gunners wore a chest parachute.
Canadian Aviation Blog