Ultra Man. See Gary Concord.

Uncle Sam. Ezra Smith, a patriotic American, tries to oppose a group of fascists calling themselves the “Purple Shirts.” For his troubles he gets shot dead. His son Buddy, heart-broken, runs away into the nearby desert. Moments later he hears “Yankee Doodle” being whistled, and then meets Uncle Sam, the embodiment of American patriotism. Uncle Sam goes on to kick butt and take names for the American way. He has superstrength, can perform Hulk-leaps, can’t be photographed, and has limited precognition.
First Appearance: National Comics #1 (Quality)

Unknown Soldier. The mysterious Unknown Soldier, nameless though self-described as “the spirit of the boys who died to see that our nation (that is, the USA) shall live forever,” shows up wherever things look worst for democracy. He fights for the good guys, naturally. He has superstrength,  and flight, and carries a “nitro gun” whose bullets are explosive.
First Appearance: Our Flag #2 (Ace)

Ur the Caveboy. Ur is a plucky and smart blond caveboy who discovers fire in a tree struck by lightning and uses his new discovery to help him and his family against various vicious dinosaurs.
First Appearance: New Fun Comics #1 (DC)

USA. This nameless woman was a USO volunteer and dancer in her civilian life. But she's a patriotic woman, and when danger threatens the USA or its citizens or soldiers, she puts on a costume and fights crime. She uses a flame-throwing "liberty torch" but has no superpowers.
First Appearance: Feature Comics #42 (Quality)

U.S. Jones. The nameless and originless U.S. Jones is a patriot and a crimefighter.
First Appearance: U.S. Jones #1 (Fox)

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