T20 Medium Tank T20 Medium Tank The Medium Tank T20 was part of a series of medium tanks designed by the United States during the Second World War, to be the successor to the Medium Tank M4 "Sherman", and culminated in the M26 Pershing. Almost immediately after the M4 Sherman was standardized, the US Ordnance Department started work on a successor. The Ordnance Department had already been working on heavily armored infantry tank design for the British, using M4 parts. The new project was started on the 25 May 1942, it was originally designated M4X. Starting with the T20, the Ordnance Department initially
Opposition to the war in Afghanistan (2001–2014) entering an eleventh year on October 7, 2011 and marking for the U.S. the longest period of sustained warfare in its history – greater than the time the United States was involved in World War I, World War II and the Korean War combined.<ref name="War and Sacrifice in the Post-9/11 Era"></ref> The war in Afghanistan surpassed the length of official U.S. participation in the Vietnam War, 8 years and 5 months, in the spring of 2010 to become the longest-running U.S. war ever. According to a study by the RAND Corporation, an American think tank working for the U.S. military,