1 PDR Hotchkiss Balloon Gun at the Watertown Arsenal Model E 1916 37mm (2)-tile
The Mark 10 1-pounder Pom Pom (Model E Hotchkiss), seen at Watertown Arsenal in 1916 with its deck penetrating naval mount. Note its water jacket and ability to go almost max vertical. The gun itself, in earlier formats with a more limited mounting, had been used by the Navy as far back as the Spanish-American War.