A German submarine, especially the ones that attacked ships in the Atlantic during the First and Second World Wars. English uses this word almost only for German submarines — an American or British one is just 'a submarine', never 'a U-boat'.

A German submarine一種德國潛艇，especially the ones特別是指 during the First and Second World Wars一、二次世界大戰期間 in the Atlantic在大西洋 that attacked ships攻擊船隻的那些。English uses this word英語用這個字 almost only for German submarines幾乎只指德國潛艇——an American or British one美國或英國的潛艇 is just 'a submarine'就只說 'a submarine'，never 'a U-boat'絕不說 'a U-boat'。

So the word is really a history word: it comes with wartime attached, and you meet it in history books, war films, documentaries, and museums. The 'U' is not English at all; it is the start of the German word Unterseeboot, 'under-sea-boat'.

So所以 the word這個字 is really其實是 a history word一個歷史字：it comes with wartime attached它自帶戰爭年代的氣味，and而 in history books在歷史書、war films戰爭片、documentaries紀錄片 and museums和博物館裡 you meet it你會遇到它。The 'U'這個 'U' is not English at all完全不是英語；it is the German word它是德語字 Unterseeboot 的 the start開頭，'under-sea-boat'「海面下的船」。

Because U-boats hunted in groups and sank supply ships, English also picked up 'wolf pack' from the same story. Note that the word is always hyphenated and the U stays capital, and the plural is simply U-boats.

Because因為 U-boats U 型潛艇 hunted in groups成群獵殺、and sank supply ships擊沉補給船，English also英語也 from the same story從同一段故事裡 picked up 'wolf pack'撿來了 'wolf pack'（狼群）這個說法。Note that注意：the word is always hyphenated這個字一定帶連字號，and the U stays capital而且 U 保持大寫，and the plural複數 is simply U-boats就是 U-boats。