In 1983, the T-55M and T-55AM tank upgrade program also added the ability to some tanks to fire the 9K116-1 "Bastion" guided missile system (NATO reporting name AT-10 Stabber), for long-range engagements of tanks and low-flying helicopters. The anti-tank missile is encased in the 3UBK10-1 shell, which is handled, loaded, and fired exactly like a conventional tank gun round. 1.5 seconds after firing, a laser guidance window in the tail of the round is uncovered, and its rocket engine ignites to burn for up to six seconds, with a total missile flight time of up to 41 seconds. The missile is very expensive, about half the price of a T-55M tank, but allows the venerable 100 mm gun to engage modern main battle tanks.