When the French occupied the Mauser factory in April 1945, they found all the tooling to produce .22 caliber rifles still in place and in good order (among other things). The French military did not have a proper training rifle at the time, and they decided to have Mauser design a produce one. The result, adopted for production in August 1945, was essentially a Mauser KKW action with the detachable magazine from the Mauser 410B and a rear-mounted aperture sight. About 10,500 of these Model 45 rifles were made at Mauser by June 1946, when production was shut down in preparation for the demolition of most of the Mauser buildings.
The tooling and incomplete parts fort he rifle were relocated to the MAS factory at St Etienne, where production resumed and another approximately 30,000 were made. The MAS-45 would serve as a standard French training rifle until he 1970s, and remained in limited use afterwards (even to this day, in fact).
To see some of the French drill and shooting, check out Bloke on the Range’s video on the MAS-45: