Type XXI submarines were a class of German diesel–electric Elektroboot (German: "electric boat") submarines designed during the Second World War. One hundred and eighteen were completed, with four being combat-ready. During the war only two were put into active service and went on patrols, but these were not used in combat.

The Type 21 frigate, or Amazon-class frigate, was a British Royal Navy general-purpose escort that was designed in the late 1960s, built in the 1970s and served throughout the 1980s into the 1990s. [1]

21型巡防舰也称为亚马逊级巡防舰、女将级巡防舰，是英国皇家海军于1960年代晚期為取代豹级巡防舰而建造的护航巡防舰 [1] ，曾參與福克蘭戰爭 [2] ，在皇家海軍一直服役到1990年代，有六艘在退役後轉售給巴基斯坦，稱為塔里克級驅逐艦。

Type 21 can refer to: Type 21 frigate, or Amazon-class frigate, a late-20th-century escort vessel of the Royal Navy. Type 021-class missile boat, a Chinese missile-firing naval vessel first produced in about 1975, and still in production. Type XXI submarine, a German technologically advanced submarine produced in 1945.

21型潜艇（又称：XXI型潜艇），是 德国 在 第二次世界大战 期间设计和使用的一型柴电潜艇。 21型潜艇是世界上第一艘真正意义上的的“潜”艇，以潜在水下巡逻和作战为宗旨 [1]。 其首次使用了通气管装置，实现了潜艇向水下航行为主的基本性能的转变，推动了二战后世界各国潜艇技术的迅速发展，被认为是现代潜艇技术发展过程中的第三个里程碑 [2]。 21型潜艇设计师为瓦尔特教授，1943年开始研制，首艇1944年5月12日下水，1944年6月27日服役 [3]。 二战一开始，自知 …

With a new rapid reloading hydraulic system, the Type XXI could launch three six torpedo salvos or eighteen torpedoes in just under 20 minutes; whereas it took over ten minutes to reload just one tube on the Type VIIC.

XXI級潛艇 （德語：Klasse XXI 、或稱 Typ XXI）是 納粹德國海軍 在 第二次世界大戰 後期使用的一級 潛艇，也是世上第一種完全為水下作戰設計、而非以往為攻擊和躲避水面艦攻擊才下潛的潛艇，為近代潛艇的雛型。 二次大戰中，於1939年開始的 大西洋海戰，德國使用的主力潛艇— VII級潛艇 在戰場上已逐漸顯得過時，因此海軍潛艇總司令 卡爾·鄧尼茲 將VIIC型和 IX級潛艇 的建造計畫變更，全力將資源投入於高速新式潛艇的建造。 XXI級潛艇改進了德軍舊有的電池容量，約 …

The Type 21 frigate, or Amazon-class frigate, was a Royal Navy general-purpose escort that was designed in the late 1960s, built in the 1970s and served throughout the 1980s into the 1990s. In the mid-1960s, the Royal Navy had a requirement for a replacement for the diesel-powered Leopard-class...

Type XXI U-boats, also known as " Elektroboote " (German: "electric boats"), were the first submarines designed to operate primarily submerged, rather than as surface ships that could submerge as a means to escape detection or launch an attack. The key improvement in the Type XXI was greatly increased battery capacity, roughly triple the Type VIIC.

2020年11月13日 · More than 250 feet long and displacing 1,620 tons, the Type XXI packed six hydraulically-reloaded torpedo tubes capable of firing more than 23 stored torpedoes. This arsenal could turn a convoy...