From the draft of my book on cannon and their ammo:
37 x 136R USN 1 Pounder Mk 6, Heavy
This cartridge was originally designed for a manually-loaded Hotchkiss gun which entered USN service in about 1890 and was also used in various other guns and sub-calibre training systems. It was adopted for two automatic weapons in the first few years of the 20th century: an enlarged Maxim "Pom-pom" known as the One Pounder Maxim-Nordenfelt, Heavy, Mk 1 (later designated 1 pdr Mk 6), which during World War 1 was ordered in large numbers for the USN; and another US automatic cannon developed by Samuel N McClean (of Lewis Gun fame). Although the gas-operated McClean gun failed to be adopted by the USA, a sale to Russia (who called it the "Maklen" gun) during World War 1 of just over 200 guns subsequently led to them being widely distributed.
The brass cartridge case was rimmed and slightly bottlenecked. Various projectiles were used, but all seem to have been of the base-fuzed steel pointed type. The overall length of the round was 210 mm and the weight was around 600 g. The standard projectile weight was 476 g and the MV 640 m/s from an L/42.5 barrel.