In World War II, the United States had outstanding fighters like the P-51 Mustang and the P-47 Thunderbolt. Allies tossed in excellent aircraft as well, like the Spitfire.
But while the Allies won the air-to-air battle against the Axis, it doesn't mean that the ground troops could forego ground-based air defense.
The U.S. had one weapon that they used for that role — especially front-line grunts. It was the M2 machine gun, known as "Ma Deuce." One could do some serious damage, firing up to 635 rounds per minute according to the FN website.
Now imagine what four of these could do to troops — or anything short of an armored vehicle or bunker, come to think of it.
The M45 Quadmount, with four M2 heavy machine guns, on a half-track. (Photo from Wikimedia Commons)
In World War II, the United States deployed the M45 Quadmount, with four M2s, each of which were fed by a 200-round drum of ammo. As an anti-aircraft weapon, it was fierce against prop-driven planes like the Me-109, the FW-190, and the Ju-87.
However, grunts often don't see what a weapon was designed to do. They quickly can come up with "off-label" uses for weapons they are issued, and the M45 Quadmount — initially designed to kill Axis planes — soon was used on Axis ground targets.
The system soon got nicknames like "Meat Chopper." The M45 mount was used on trailers, but also on the M16 half-track, where it was called the MGMC for "Multiple Gun Motor Carriage" — in essence, a self-propelled anti-aircraft gun. One version was even tested on the chassis of the M3 light tank — but that version didn't go into production.
M16 MGMC. (Photo by US Army Signal Corps)
The M45 "Meat Chopper" didn't leave when World War II ended. In fact, it managed to stick around for the Korean War and the Vietnam War — in both cases serving as a very deadly infantry-support platform.