The Model 1918 had all of the major components in place that would keep the
Browning .50 caliber in service in American military arsenals into the 21st century.
Some changes were made in 1933 in a joint effort by the Army and Navy. Two of the the improvements were a heavier bottom plate that better supported the receiver side plates and an increase in the ammunition lift capacity to 17 pounds, the latter in anticipation of longer and heavier linked ammunition belts. The resulting gun was designated the M2 Aircraft. (Source, image above and below, Machine Guns, by G. Chinn)

.50 caliber Browning M2 aircraft machine gun on training hard mount.

Stats for the M2 aircraft. The ground gun figures and photos are shown for comparison. The flexible ground gun (HB) has integral spadegrips. The aircraft version requires an adapter which incorporates the handles and trigger mechanism.

The ground Browning .50 caliber M2 HB on an M3 tripod.

An armorer working on a .50 M2

Blowup of the M2. Click to enlarge.

A belly gunner on a B-24L. In an attempt to reduce weight, the Sperry ball turret was eliminated and a single, ball-mounted .50 was substituted. The Sperry turret returned in the B-24M model.

B-25 nose gun adapter, a Mark 6 variant..

B-25 Mitchell. Most B-25s featured
this greenhouse nose position.

Two views of the B-25 adapter installed on M2.

ANM2 .50s and one ANM2 .30 (at bottom)
on a workbench. Source - National Archives.

A B-25 Mitchell fitted with eight .50s for strafing.
This photo is from the Chinn book.

A26B Invader over France.