The Soviet-designed, Russian-manufactured 2K12 KUB surface-to-air missile (SAM) system, also known by the NATO reporting name SA-6 GAINFUL, is a highly mobile, still very capable platform for attacking aircraft at low to medium altitude. The original system mounted four 9M336 missiles (also known as the 3M9) on a single tracked transport-erector-launcher (TEL), slightly reminiscent of the U.S. MIM-23 Hawk. It really should be considered the lead of a series of SAM systems, with NATO reporting names including:
- SA-6 GAINFUL
- SA-6B GAINFUL Mod 1
- SA-8 GECKO
- SA-11 GADFLY
Its first versions saw action in the 1973 Arab-Israeli War, also called (Yom Kippur War). Its designers had incremental improvements ready, as when the Israelis overloaded the original per-TEL radars, they were immediately surprised by the SA-6 also having an electro-optically assisted visual engagement mode. Shortly afterwards, however, the Soviets added an engagement radar to each TEL.
The resulting TELAR (Transporter-Erector-Launcher And Radar) became known by the NATO reporting name SA-8 Gecko.
Eventually, all components were replaced by the SA-11 GADFLY system, still a derivative.
In Soviet service, the antecedents and successors of the KUB were seen as a divisional-level air defense system, replacing the S-60 radar-guided 57mm anti-aircraft artillery system. Missile design began the Toropov design bureau at Tushino in 1959. 
Actual testing of the 9M9 missile itself did not begin until 1965, partially because Toporov had received a Chinese contract to evaluate the U.S. AIM-9 Sidewinder in SAM applications. 
It went into Soviet operational service in 1970.
The original missile is has two solid-fuel stages. Visually, it is quite different from earlier Soviet missiles, with four "long slender tube air inlet ducts mounted mid-body between the wings. At mid-body, there are four clipped movable triangular wings for pitch and yaw control. Just forward of the jettisonable boat-tail are four in-line clipped delta fins with ailerons for roll control. The missile is 5.8 m long, has a body diameter of 0.34 m and with a 59 kg HE fragmentation warhead, weighs 600 kg at launch."
It has both proximity and contact fuses, which are armed after the first 50 meters of flight. 50 meters of flight. and has a minimum effective range of 3,000 m.
Electronics and Electro-optics
Missile guidance uses radio command guidance with semi-active radar homing.
When under the control of the STRAIGHT FLUSH radar, it can engage targets at a minimum 3KM range and an altitude of 100 meters (80 meters when in electro-optical guidance). the minimum engagement height is 100m when using the fire control (STRAIGHT FLUSH) radar and 80m when in the optical tracking mode. Maximum range is 24KM and maximum altitude 11 KM. The STRAIGHT FLUSH has a maximum range of 55 - 75km and a 10,000m altitude capability depending upon the conditions and target size. It is multifunction, although is designed to work with the separate LONG TRACK search radar, operated at missile regiment level.
Nevertheless, it can do some search, especially at low altitude. It then tracks and illuminates the target, performs Doppler identification-friend-or-foe, and may also track its own missiles. 
The engagement radars can send up to three missiles at a single target. To maintain radar silence, or defeat radar jamming, it has a backup electro-optical tracking with television and a laser rangefinder.
First seen in the 1973 Arab-Israeli War, it was a surprise and a partial success. Its backup optical guidance mode was an unpleasant surprise to the Israelis, who found jamming useless against it, and had to make the launchers a high priority of ground combat.
In 1999, the system still was effective in Kosovo.  While there has not been official confirmation, the SA-6 may have been involved in shooting down a U.S. F-117 Nighthawk "stealth" fighter over Kosovo in 1999. Actual detection may have used an older long-wave radar, with the SA-6 fired using electro-optical guidance. When the missile threatened the F-117, the latter may have maneuvered away, and into the path of fighters or AAA. 
It may be part of Iranian air defense, and is known to be part of the air defenses of Libya. While there are newer generations of Russian missile, it remains a credible threat at low altitude.
- ↑ KUB is Russian for "cube"
- ↑ 2.0 2.1 2.2 2.3 2.4 , SA-6 GAINFUL, The Hawk Website
- ↑ 3.0 3.1 3.2 Globalsecurity.org, ZRK-SD Kub 3M9, SA-6 Gainful
- ↑ Anthony Cordesman (August, 2000), The Effectiveness of the NATO Tactical Air and Missile Campaign Against Serbian Air and Ground Forces in Kosovo: A Working Paper, Center for Strategic and International Studies
- ↑ A Lost Illusion