The 9M111 Fagot (bassoon) is a SACLOS (Semi-Automatic Command to Line of Sight) wire-guided anti-tank missile of the Soviet Union. "9M111" is the GRAU designation of the missile. Its NATO reporting name is AT-4 Spigot.

The missile is stored and carried in a container/launch tube. It is fired from the 9P135 launcher post - a simple tripod. A 9S451 guidance box is fitted to the tripod - with the missile sitting just above.

The 9Sh119 sight is fitted to the left side (from the gunners POV). The complete launcher system weighs 22.5 kg.

The gunner lays prone while firing. The system can engage moving targets providing they are travelling at less than 60 km/h. The launcher post can traverse through 360 degrees horizontally, and +/- 20 degrees in elevation. The sight has a magnification of 10x and a 5 degree field of view. Up to 3 missiles a minute can be fired from a launcher post.

The system uses a gas generator to push the missile out of the launch tube - the gas also exits from the rear of the launch tube in a similar manner to a recoilless rifle. The missile leaves the launch tube at 80 m/s.

It is quickly accelerated to 186 m/s by its solid fuel motor. This initial high speed reduces the deadzone of the missile, since it can be launched directly at the target, rather than in an upward arc.

The launcher tracks the position of an incandescent infrared bulb on the back of the missile relative to the target - and transmits appropriate commands to the missile via a thin wire that trails behind the missile. The SACLOS guidance system has many benefits over MCLOS, with the accuracy of the system stated as 90% in some sources, though its performance is probably comparable to the TOW or the later SACLOS versions of the AT-3 Sagger.