Tanks of the United States John J. Pershing who led the American Expeditionary Force in Europe in World War I, it was designed and came out at the end of World War II and was used in the Korean Conflict. In May 1946, due to changing conceptions of the U.S. Army's tank needs, the M26 was reclassified as a medium tank. Designed as a heavy tank, the Pershing was a significant upgrade from the M4 Sherman in terms of firepower with its 90 mm gun and protection. On the other hand, its mobility was unsatisfactory for a medium tank (it used the same engine that
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,