DD or duplex drive tanks, nicknamed "Donald Duck tanks", [1] were a type of amphibious swimming tank developed by the British during the Second World War. The phrase is mostly used for the Duplex Drive variant of the M4 Sherman medium tank, that was used by the Western Allies during and after the Normandy Landings in June 1944.

Sherman DD: (for “Duplex Drive”, but the crews nicknamed it “Donald Duck”) This special-purpose vehicle was specifically developed for D-Day. It featured a flexible waterproof canvas skirt fixed on the mudguard, reinforced with a folding wooden and metal frame.

兩棲登陸戰車（DD戰車）：兩棲坦克（Duplex Drive，DD），改裝車輛分別基於M4A1、M4A2、M4A3、M4A4。二戰中英軍使用的雪曼兩棲坦克基於M4A1（75）、M4A2（75）、M4A4改裝，美軍只使用了用英國套件改裝的M4A1（75）。

m4a2中期型：驾驶员和无线电员前方还未加装附加装甲，可以看见其特有的焊接件特征，而非m4和m4a1使用的铸造件。 M4A2中期和后期车体前部的对比，可以看到这辆中期型的M4A2前方加装了附加装甲。

m4中型坦克有8种改进型：m4a1、m4a2、m4a3、m4a3e2、m4a3e8、m4a4、m4a6和m4e6，几种型号之间的主要区别在于火炮和发动机类型有所不同。 此外，行动装置也有所改进。

英国利用m4(75)、m4a2(75)、m4a3(75)w和m4a4改装17磅mks iv/vii加农炮，以提高m4系列的反坦克火力，能在1000米处贯穿虎式坦克的正面装甲。 M4和M4A4为主要改装用底盘。

Of the 693 DD conversions done by the British, 293 were based on the M4A2 or Sherman III. These appear to have been converted in the second half of 1944, with the program completed in December. As mentioned previously, Sherman III DDs don't appear to have become available in numbers until early 1945.

m4a2式坦克曾援助苏联，获得苏联人高度评价，其闭式散热器具有在较低功率下有效利用发动机功率的特点，独特的五叶式散热器风扇扇叶角度不一，高速运转时可降低噪音，使坦克具有更好的隐蔽性。

THE DD OR DUPLEX DRIVE TANK "One of the most secret and startling devices" that had yet been evolved. (Above: Valentine DD tank. Though M4A2 Sherman DD tanks were used during the Normandy landings, most crews conducted their early training on the earlier Valentine DD.)

Sherman DD (Duplex drive) – Amphibious M4 Variant produced by US and British shops using M4A1, M4A2 and M4A4 donor vehicles. Sherman Firefly – About 2,000 M4s (Firefly IC) and M4A4s (Firefly VC) were re-armed by the British in 1944 with their 17-pounder (76.2 mm) guns as the Sherman Firefly.