The T-55A is a Soviet medium tank, in many ways a development of the T-54A. This variant includes significant additions such as the "PAZ/FVU" NBC protection system (a series of internal liners and chemical filters which protect from weapons of mass destruction), a new engine and an STP-2 "Tsyklon" two-plane stabiliser. Although the original production models lacked an anti-air DShK Machinegun, the threat of the nascent Attack Helicopter 🚁 convinced Soviet leadership to reintegrate it. Regardless, most Soviet divisional commanders had the DShK reinstalled one way or another.