and steeply sloped frontal armor of later German designs such as the Tiger and Panther. The problem of the main gun performance was somewhat remedied with High Velocity Armor Piercing (HVAP) ammunition beginning in fall 1944, which allowed the 76 mm gun to achieve greater armor penetration, but this was never available in quantity. The 76 mm gun with standard ammunition could penetrate the frontal turret armor of Panther tanks only at very close ranges, whereas the HVAP ammunition gave it a possibility of effectively engaging some of the heavier German tanks and theoretically penetrating the front of the Panther turret at ranges of about . Armor The armor of the M18 Hellcat was quite light to facilitate its high speed, and only provided protection from small arms fire. The lower hull armor was thick all around, vertical on the sides, but sloped at 35 degrees from the vertical at the lower rear and angled twice at the lower front to form a nearly rounded shape; 53 degrees from the vertical and then 24 degrees from the vertical. The hull floor was only thick. The upper front hull also had an angled construction to form the Hellcat's sloping glacis; two plates were angled at 38 and 64 degrees from the vertical, respectively. The upper hull armor was also thick, being angled at 23 degrees from the vertical on the sides and 13 degrees from the vertical at the rear. The hull roof was The cast turret of the Hellcat was thick on the front (at a 23 degree angle from the vertical) and thick on the sides (also at a 23 degree angle from the vertical) and rear (angled at 9 degrees from the vertical) The front of the turret was further protected by a rounded cast gun mantlet which was thick. Another disadvantage of the M18 was its very light armor protection and open-topped turret. In testing of the T70 for possible use as a light tank, 9 out of 30 armor-piercing .30 caliber bullets penetrated the side of the turret at a range of . The open-topped turret—a characteristic which it shared with all American tank destroyers—left the crew exposed to snipers, grenades, and shell fragments, however it gave the crew excellent visibility, which was of importance in the killing of tanks, the intent of tank destroyers being primarily ambush weapons. The doctrinal priority of high speed at