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In 1959 the German military first adopted the Spanish CETME as its standard infantry rifle, because it was able to acquire a license to manufacture the guns domestically (something FN had been unwilling to grant for the FAL). The European rights to the CETME were at that time owned by NWM in the Netherlands, and Germany negotiated a trade to allow its own production. That production was undertaken by two different firms - Rheinmetall and Heckler & Koch.
Ultimately Rheinmetall's quality was sub-par, and production of the G3 would transfer entirely to H&K - but not before Rheinmetall made a number of international commercial sales of the gun. This particular example is one of a batch purchased by the Indonesian Air Force, and it sports a collapsing stock that was made between 1959 and 1961 - substantially predating the H&K collapsing stocks.
These Indonesian rifles were used by Indonesian paratroops in fighting on Papua New Guinea, where the Indonesian military was attempting to take over control of the country from the fledgling independence movement (which was supported by the Dutch government). This rifle was captured by the Papua Volunteer Corps in the early 1960s, and ultimately handed over to the Dutch military, from whence it found its way into the Dutch Military Museum.
Thanks to the Dutch National Military Museum for allowing me access to film this rifle! Check them out at: https://www.nmm.nl