米國的航艦自CVN-68起都用人名, 攻擊型潛艦自SSN-688起向來以都市命名, Trident 則是以最尊貴的州名 來命名. 只有這麼一隻SSN-21沒任何規矩, 冒出來一個奇特的序號21與名字Seawolf. 下面是 Google 找到的
The name of this ship was never officially confirmed because the name was given by Admiral Watkins who wanted to return to the old tradition that attack submarines should be named after animals living in the oceans. But he was not authorized to do that because the names of ships are announced by a SECNAV Instruction.
Another mistake is the ship’s number, SSN 21. This number was created by Vice Admiral N. Thunman. He said that the submarine for the 21st century should be named SSN 21. By doing so he made the mistake that every ship’s number can only be given once and the number "21" was already given in 1912.