U-boat – A German submarine. Use submarine unless directly referring to a German vessel of World War I or World War II vintage.
undersecretary – One word, lowercase unless preceding a name in a title.
underway – One word in all uses: The Navy’s maneuvers are underway.
Uniform Code of Military Justice – Spell out on first reference, then use UCMJ.
United Service Organization – USO is acceptable in all references.
United States – Refers to the 50 states and the District of Columbia. Use the abbreviation U.S. in texts and US in headlines.
URL – Acceptable in all references to Uniform Resource Locator. When the URL doesn’t fit on one line, break into two or more lines without a hyphen or other punctuation. In printed or downloaded documents use the complete URL: https://www.militaryonesource.mil.
U.S. – The abbreviation is acceptable as a noun or adjective for the United States. Use U.S. in texts and US in headlines
USA – No periods or spaces in the abbreviation for the United States of America.
U.S. Army, U.S. Marine Corps, U.S. Navy, U.S. Air Force, U.S. Space Force, U.S. Coast Guard - or Army, Navy, Marines, Air Force, Space Force or Coast Guard. Capitalize in all uses when referring to U.S. forces.
USS – Use USS when it precedes the name of a United States Ship, Steamer or Steamship: the USS Nimitz.