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The UD-42 was originally the design of Carl "Gus" Swebilius, who was at the time (1940) working for the High Standard company. It failed to attract interest form the US military, but was appealing to the Dutch government for arming their East Indies colonies. A contract for 15,000 guns was signed, but High Standard did not have the production capacity to fill the order. Instead, the United Defense company took up the contract, and then subcontracted the actual manufacture to Marlin.
Production startup issues slowed production, however, and it was April 1941 before the first gun was completed. Delivery would not come before the Japanese completed their conquest of the Dutch East Indies, and the guns were repurposed. They were ideal for OSS and SOE use in supplying Resistance organizations in occupied Europe, and the bulk of the guns would be distributed in this way, from Greece to Norway and most everywhere in between. This particular example is in Holland, with provenance back to an OSS covert supply drop.
Many thanks to the anonymous collector who let me take a look at this piece and bring you a video on it!