The T3 front grip doubled as an adjustable monopod and the two-piece padded T3 shoulder cradle could swing down and to the rear as a bipod for the gunner.

[5] During World War II, the U.S. Army's Artillery Section was working on a 105 mm recoilless cannon, based on captured models of the German 10.5 cm Leichtgeschütz 40 that used a plastic blow out plug in the cartridge case.

At the same time, there was a freelance research by the U.S. Army's Infantry Section of a man-portable recoilless 57 mm cannon by two engineers, named Kroger and Musser.

Instead of a blowout plug, the infantry section's recoilless cannon used a British development, Ordnance, RCL, 3.45 in developed by Dennistoun Burney, from in which the cartridge case had hundreds of small holes in the side walls with a lining of plastic on the inside of the cartridge case walls to keep water and other elements out until the round was fired.

[6][note 2] The "Kromuskit", as the new 57 mm weapon was called (a word play on the engineers' family names) was officially designated the T15 and first tested in November 1943.

[citation needed] The first fifty[9] production M18 57 mm cannons and ammunition were rushed from the factories to the European theater in March 1945.

[12][13][note 4] In the Pacific Theater, the new lightweight 57 mm cannon was an absolute success as "pocket artillery" for the soldiers of U.S. Army infantry units that were issued the M18.

It was first used in the Pacific Theater during the Battle of Okinawa on 9 June 1945, and proved with its HE and white phosphorus rounds it was the perfect weapon for the hard fighting that took place against the dug-in Japanese in the hills of that island.

[16] For anti-tank tasks, however, the M18 was too weak; the Soviet-built T-34 tank was extremely hard to penetrate even for the 2.36-inch (60 mm) Bazooka of World War II.

It was able to use the NATO-standard M74 tripod, and proved with its HE and white phosphorus rounds it was the perfect weapon for the hard fighting that took place against dug-in People's Army of Vietnam forces.