A Floating Dry-Dock?

 

Curious. This box had a series of Slide Mounts, each with a 35mm Black and White negative mounted in them. How rare. The seller claimed that they dated from 1937...and that might be reasonable.

This image had no description, but appears to be a floating dry-dock, so... COULD be the USS ARD-1. Or maybe something else.

Bonus :