The Spanwire Anti-Slack Device prevents bird-caging by keeping tension on the section of the wire rope located between the ASD and the winch drum. The ASD uses a tensioning system that converts motor torque into constant wire rope tension of not less than 1,000 pounds at a rated line speed of 240 feet per minute. When the ASD is on, the AC induction motor is started and drives a slip drum, with a powered squeeze sheave driven in the payout direction by an air clutch. To hold the wire rope in the sheave (to transmit torque) a set of rollers are actuated by an air bag to squeeze the sheave on the wire rope. This pulls on the wire rope, always maintaining the minimum rated line tension. When the ASD is not energized, it doesn’t grip the rope nor is it driven in the payout direction, essentially a normal freewheeling fairlead sheave.