The 9K111 Fagot is an anti-tank missile of Soviet origin. The 9K111 is better known by its NATO designation AT-4 Spigot. It was developed in the late 1960's as a more compact and more effective system than the 9K11 Malyutka system. The 9K111 is a medium range system and is in the same league as the French Milan system.

The 9K111 Fagot sytem is a man portable system that uses a reuseable ground launcher. The 9M111 missile is transported in and launched from a container. The missile has a booster charge and sustainer rocket motor. Four small vanes at the front and four large wings in the middle provide stability during launch. The 9M111 is wire guided and features SACLOS guidance. The 9P135 lightweight tripod launcher includes an optical sight system and computing mechanism. The same launcher can be used with the larger and longer range 9M113 Konkurs missile.

The 9K111 can be used to take out any armored vehicle except modern tanks over the frontal arc. The original missile has a penetration of 400mm RHA, with the latest missile capable of penetrating up to 600mm RHA. The maximum range is 2 km for the original missile and 2.5 km for the improved missiles. If not obscured by smoke the SACLOS guidedance system ensures a good chance to hit the target, even when the target is moving.

The 9K111 is a very mobile system. The tripod launcher with a missile ready to fire weighs less than 40 kg. When the load is divided over multiple persons the 9K111 may even be transported over long distances by infantry. Normally the 9K111 is transported by vehicle and employed away from the vehicle. The 9K111 launcher has also been pintle mounted on various armored vehicles. On the BMP-1P and BMD-1P the pintle mounted launcher replaced the 9M14 Malyutka launcher that was mounted on the 73mm low pressure gun. The 9K111 is not used on aircraft or in a naval role.

The 9K111 was widely used by the USSR and most Eastern European nations during the Cold War. The 9K111 was also widely exported, but not the extent of the earlier 9K11 Malyutka system. The 9K111 remains in use and production and is expected to remain in use even though more modern systems are available.