On the occasion of the commemoration of the 75th anniversary of D-Day, a friend of mine and I were discussing the fearsome German weapons that our invading force faced on Omaha Beach.
I mentioned to him that I had recently learned how effective (and brutal) the German machine guns were that day (especially the M42).
To my surprise, he agreed with me and said that he personally saw the weapon in the hands of the Viet Cong, 15-20 years later.(He did three Viet Nam tours, as a member of the 101st Airbourne Division).
Our troops were so impressed with this weapon; they preferred it to their own M60 machine gun.
The following article discusses these weapons (especially the M34, the predecessor to the M42). I guess the Soviets had all these weapons stockpiled, and it didn't cost them anything to pass them over to North Vietnam.
https://www.google.com/search?q=101st+division+viet+nam& oq=101st+division+viet+nam& aqs=chrome..69i57j0.24642j0j8& sourceid=chrome& ie=UTF-8