 ; tank destroyers were to engage numbers of enemy tanks that broke through friendly lines.McNair approved the 76 mm upgrade to the M4 Sherman and production of the 90 mm gun-armed M36 tank destroyer, but he at first staunchly opposed mass production of the T20 medium tank series and its descendants, the T25 and T26 (which would eventually become the M26 Pershing) during the crucial period of 1943 because they did not meet the two criteria of the Army Ground Forces for accepting new equipment; they were not "battle worthy," and he saw no "battle need" for them.In fall 1943, Lieutenant General Devers, commander of U.S. forces in the European Theater of Operations (ETO), asked for 250 T26 tanks for use in the invasion of France; McNair refused, citing the fact that he believed the M4 was adequate.