United Defense M42 [SEP] conflict
supply British-led partisan forces on the island of Crete, where it was used extensively. It also saw use among the partisan forces of the Italian and French Resistance. Some of them were transferred to Dai Li's regular resistance forces in China for use against the Japanese invasion. The United Defense M42 was issued for use by Filipino troops under the Philippine Army and Philippine Constabulary during World War II from 1942 through the Post-World War II era until the 1960s and was used by the local recognized guerrillas from 1942 to
for the British government, further development of the submachine gun was handled the United Defense Supply Corporation founded by Pope and Jackson of the British Purchasing Commission. United Defense did not have any manufacturing capability so it contracted with Marlin Firearms to have the M42 actually built. 
The UD M42 was promoted as a replacement for the Thompson submachine gun, which the U.S. military considered both expensive and complicated to produce. Made in both 9×19mm Parabellum and .45 ACP prototypes, the 9 mm version was the only one to ever see