Here is a piece you don't see every day. After WW1 the Japanese contracted the Bergmann company (via SIG in Switzerland) to produce a 1920 version of the Bergmann sub machine gun (MP 18, I)
These machine guns had a special detachable collar used for attaching the Japanese bayonet. I don't know how many survived but I would think not many.
The German based Bergmann Company was forced to cease manufacture of the M.P. 18,I. The company negotiated a licensing agreement with the Schweizer Industrie Gesellschaft (SIG) to manufacture the M.P. 18,I in Neuhausen, Switzerland. The weapon was manufactured with the modified magazine housing and box style magazine into the 1920’s principally for foreign sales. The Swiss made M.P. 18,I was marketed as the Bergmann Machine Pistol, and was produced in 7.65 mm Mauser, 7.63 mm, 9 mm Mauser and 9 mm Parabellum. The weapons were distributed by the Swiss firm Societe Industrialle Suisse. The majority of the weapon’s sales were made to Japan chambered for the 7.63 mm cartridge. The Japanese contract guns were designated as the Type BE. There were at least two variants of the Japanese contract guns. One style had a removable collar that fitted on the barrel jacket for mounting a Japanese service bayonet; the second type was made with and without the bayonet feature, and were marked with Japanese characters. Over 25,000 post WWI M.P. 18,I weapons (modified) were produced for export.