[Stellan Bojerud (RIP)]

Hmm? The British Mk 1 (riveted) platform or carriage was copied in USA and designed M 1. Most of these issued as lend-lease to other countries.

The welded version of the British Mk 1 carriage developed in USA was known as M 2 and in a later version M 2 A1.

Photo: US 40 mm AA gun M 1 on carriage M 2.