A little bit of a mystery.
There are two or three "on-line" experts who have slightly contradicting ideas on this one.
I have only this to go by as there is nothing on a water cooled MG15 in any of my machine gun books.
i. Produced by Germany in Romania (never fielded kept in storage) exported to UK then by IMA to the US as parts kits.
ii. France to Romania in WW2, converted for export by German officials, Romania changed sides never fielded, and guns stayed in storage - then to US as parts kits.
It is an MG15 machine gun converted to ground use, with a water cooled front end.
The receiver is marked 1943 but has been stamped ST61.
All MG15 parts are waffen marked and also have the more imperial looking eagla sans swastika.
The water cooled parts are rougher finish and unmarked - no waffens or eagles and only mismatched numbers.
There are no markings on the bipod.
Would love to see any pictures of it in "period" use - if anyone can find any.
The best anyone has come up with is a Romanian training manual that looks circa 1950's but could be more modern.
Quite a high ROF (1200 to 1500 RPM) - with a very violent ejection, in fact never seen anything quite like it, almost dangerous to shooter's toes appendages.
Anyway for your study and conjecture.