Thus the Panzer IV, originally intended to be a support tank, became the de facto main medium tank re-armed with a long-barreled, high velocity 75 mm gun to counter the T-34; the Panzer III, with its smaller turret ring, could not mount a gun larger than 50 mm, which had become inadequate against Allied tanks. The Germans started to develop newer, heavier tanks. This included the Panzer V Panther, which was intended to be the new main German medium tank, with comparably sloped armor to that of the T-34. The Panther tank was a compromise of various requirements. While sharing essentially the same engine as the Tiger I tank, it had better frontal armor, better gun penetration, was lighter overall and thus faster, and could handle rough terrain better than the Tigers. The trade-off was much weaker side armor; the Panther proved to be deadly in open country and shooting from long range, but was vulnerable in close-quarters combat or to flank shots.