The MP 38 was a Nazi submachine gun manufactured by Ermawerke in Erfurt, Germany in 1937. It was intended to be issued initially to the Schutzstaffel in 1938.
Vogler, a German weapons smuggler, secretly made an arms deal with Hsien-Ko, Kwok and the Tong of the Black Scorpion in 1937. Seeking his agreed-upon payment in opium resin, Volger smuggled out 600 MP 38s, along with 600,000 rounds of ammunition, from the highly-secured German factory and delivered them to China. There, Kwok killed Vogler with one of the weapons and took the supplies.
The Fourth Doctor noted the potential danger of Hsien-Ko travelling back in time while armed with an MP 38 and taking over the Chinese Empire during the time of Qin Shi Huang. (PROSE: The Shadow of Weng-Chiang)