The United States Army (USA) is the land warfare service branch of the United States Armed Forces.
History
From 1917 to 1918 the US Army (including Steve Trevor) participated in World War I, and was aided by Wonder Woman.
In 2013, Kal-El surrendered himself to the US Army after they took Lois Lane into custody, in order to turn him over to General Zod. Kal-El's surrender was conditional on Lane's release. Notably, it was the US Army that gave Kal-El the nickname "Superman."
Trivia
To be added