I was hoping to try to put together any history if possible on a couple of guns we have been restoring.

They apparently came from Puerto Rico at some point. They are 3.7cm SKC/30Us
on L. C/39 mounts.

All the gun markings match as well as all the markings on the mounts.

They both have an inconsistent number stamped on top of the ring.

516 and 639.

I cannot figure out what those would relate to.

They are defiantly hand stamped by the appearance, while all other markings
are factory pressed.

Is it possible that that could relate to a boat?

The U-516 was an IXC laid down in 1941.

It made it through the war but was part of Operation Deadlight in 46.

The U639 was a VIIC and was laid down in 41 and sunk in 43.

Both were old enough to have had a 37U gun on them, but considering the U639
was lost and the U516 was scuttled it seems unlikely that they correlate.
Unless the guns were replaced prior.

What class of boats would have been most likely to have had these guns and ended up in US control?

Any info you can supply pertaining to US boats or guns would be appreciated.

Thank You in advance
Ira

Link to Vid of what I would assume is the only Uboat gun being fired in the world. Please correct me if that is not a true statement and I will be ecstatic.
[www.youtube.com]