The Liberator carried a crew of up to 10. The pilot and co-pilot sat alongside each other in a well glazed cockpit. The navigator and bombardier, who could also double as a nose or "wiggly ear" gunner (guns mounted in the sides of the aircraft nose), sat in the nose, fronted on the pre-B-24H models with a well-framed "greenhouse" nose with some two dozen glazed panels in total, with two flexible ball-mounts built into it for forward defensive firepower using .30 caliber (7.62 mm) Browning M1919 machine guns. Later versions were fitted with a powered twin- .50 caliber (12.7 mm) M2 Browning machine gun nose turret. The radio/radar operator sat behind the pilots, facing sideways and sometimes doubled as a waist gunner. The upper gun turret, when fitted, was located just behind the cockpit, in front of the wing, and was operated by the flight engineer, who sat adjacent to the radio operator behind the pilots. In the tail, up to four crew could be located in the waist, operating waist guns, a retractable lower ball turret and a tail gun turret matching the nose turret. The waist gun hatches were provided with doors, with the ball turret required to be retractable for ground clearance when preparing to land, as well as for greater aerodynamic efficiency. The tail gunner's powered twin-gun turret was located at the end of the tail, behind the tailplane.