Before the end of World War I, the U.S.
Ordnance Department recognized that water-cooled
machine guns took up too much space inside a tank.
Consequently, the water-cooled M1917 was converted to
an air-cooled model by surrounding the barrel with a
perforated metal jacket.
As World War II approached, the
Ordnance Department was committed to developing an
air-cooled machine gun for infantry use. The result was
At 41 lbs for gun and tripod, the
M1919A4 was much lighter than the water-cooled M1917A1 (93 lbs for gun and
tripod). On the other hand, the air-cooled weapon was
unable to maintain the same level of sustained fire as
the water-cooled M1917A1, and did not have the
steadiness of accuracy as the heavier weapon. But its
light weight and ease of set-up made it much more
useful as an offensive weapon than the water-cooled
In fixed defensive positions, however,
the water-cooled M1917A1 saw much use in Korea. With
anti-freeze in the water jacket, the heavy MG was more
reliable in intense Chosin
cold, as was particularly observed in the savage
Reservoir battles. In any weather, the heavy was also
more stable and, under intense attack, its greater
sustained volume of fire was much appreciated.
Moreover, the A4 was crticized for
slowness of set-up and vulnerability of crew. To meet
these weaknesses, the M1919A6 was developed, and saw use
in WWII, Korea and