Browning M2 .50 Caliber Flexible Machine Gun.
M3 Anti-aircraft Mount
As an anti-aircraft gun on the ground. The original water-cooled version of the M2 was used on a tall AA tripod or vehicle-mounted anti-aircraft weapon on pedestal mount.. the individual M2HB's rate of fire (450–550 rounds per minute) was low for an effective anti-aircraft weapon.

L1A1, L1A2
12.7 × 99 mm Browning M2HB machine gun with a 36-inch barrel (L1A1) or 45-inch barrel (L1A2); mounted on tripods, anti-aircraft stands -Wikipedia