USN is short for the United States Navy — the part of the American armed forces that fights at sea, with ships, submarines and aircraft that fly from ships. Like most military abbreviations it belongs to writing, not to speech: it appears on uniforms, on official papers, and after a person's name to show which service they belong to, as in 'Captain Ellen Ruiz, USN'.

USN『USN』 is short for是...的縮寫 the United States Navy美國海軍——the part of the American armed forces美軍裡 that fights at sea打海戰的那個軍種, with ships, submarines and aircraft that fly from ships有軍艦、潛艦，還有從軍艦上起飛的飛機。Like most military abbreviations像大部分軍事縮寫一樣, it belongs to writing, not to speech它是用在書面，不是用在口語的: it appears on uniforms它會出現在制服上, on official papers公文上, and而且 after a person's name加在人名後面 to show which service they belong to表示他們屬於哪個軍種, as in就像 'Captain Ellen Ruiz, USN'『Captain Ellen Ruiz, USN』這樣。

When people talk, they say 'the Navy'. Each letter is said separately (U-S-N).

When people talk平常講話時, they say大家會說 'the Navy'『the Navy』（海軍）。Each letter每個字母 is said separately是分開唸的 (U-S-N)（U-S-N）。

You will also meet it beside its cousins USMC (the Marines) and USAF (the Air Force), and beside USS, which goes in front of a ship's name. Outside American contexts it is not much used, so write the full name once before using the letters.

You will also meet it你也會看到它 beside its cousins跟它的同類擺在一起 USMC (the Marines)USMC（陸戰隊） and和 USAF (the Air Force)USAF（空軍）, and而且 beside USS跟USS擺在一起, which它 goes in front of a ship's name放在軍艦名字前面。Outside American contexts在美國以外的脈絡, it is not much used這個字不太常用, so所以 write the full name once先把全名寫一次 before using the letters再用縮寫。