Krug Credit - © Mark Wade

Ramjet-powered long-range surface-to-air missile, deployed by the Soviet Union and its allies.

Preliminary work on the concept used the artillery-launched KRI flying shell (a flying laboratory used to develop ramjets and surface-to-air missiles by Bondaryuk in the mid-1950's). This eventually evolved into the 2K11 Krug surface-to-air missile. Development into an operational system was authorised by decree 188-88 of 13 February 1958. NII-20 GKRE (later NIEMI, later Antey) was prime contractor, under the management of Chief Designer V P Efremov. The 1S12 observation and targeting system was developed by V V Raizberg at NII-208 GKRE (later NIIIP); the 1S32 guidance system by I M Drize at NII-20 GKRE; the 2P24 launcher and 3M8 surface-to-air missile by L V Lyulev at OKB-8 GKAT (later EMKB Novator named for L V Lyulev); the self-propelled launcher was developed by General Designer A I Autonomov at the Kharkov Machine Works named for V A Malyshev. OKB-8 GKAT occupied a single industrial area within the OAO M I Kalinin Machine Works.

The missile had a two-stage aerodynamic layout with the cruciform wings of each stage at 45 degrees to each other. The wings and stabilisers were lightweight and easily removable for transport of the missile. The rocket was accelerated to ramjet ignition speed by four solid booster rockets. There were two surface-to-air missiles per launcher. The launcher itself was in contact with the guidance station by a radio data link; the missiles talked back over the link, indicating their readiness for launch.

The missile took six years to develop, including development of the 3Ts4 Bondaryuk ramjet, which operated on kerosene. The chief difficulty was that the ramjet only operated well at low angles of attack. Any abrupt manoeuvre would cause a reduction in thrust or even flameout. Solving this was an enormous challenge. In early tests the missile would become uncontrollable as soon as the first guidance command was received. The electronics aboard the missile were also not adequately shock- and vibration- resistant at first. There were also problems with arrangement of the guidance antennae, which would become masked as the missile manoeuvred, also causing it to go out of control.

All of these problems were eventually overcome, and the Krug was accepted for PVO service in 1964.

Maximum target speed 2880 kph. 5 minutes from arrival at a new location to launch readiness; 5 minutes required to depart in 'shoot and scoot' mode. Two missiles per launcher.

Radars: P-40 Long Track target acquisition radar, E band, range 175 km. 1S32 Pat Hand target tracking radar, H band, range 130 km. Thin Skin height finding radar, H band, range 240 km.

Manufacturer: Efremov/Lyulev. Location: Moscow. Total Mass: 2,450 kg (5,400 lb). Core Diameter: 0.86 m (2.82 ft). Total Length: 8.80 m (28.80 ft). Span: 2.56 m (8.39 ft). Standard warhead mass: 150 kg (330 lb). Maximum range: 45 km (27 mi). Guidance: Command Link + Semi-Active Radar Homing. Maximum speed: 3,060 kph (1,900 mph). Minimum range: 11 km (6 mi). Ceiling: 23,500 m (77,000 ft). Floor: 3,000 m (9,800 ft). Surveillance Radar: Long Track/E. Tracking Radar: Pat Hand/H.

The Krug-A 2K11A version of the missile was accepted in 1967. This reduced the minimum altitude capability of the system to targets flying as low as 250 m.

Boost Propulsion: Solid rocket. Boost engine: 4 x solid rocket. Cruise Propulsion: Bondaryuk RD-058 Ramjet.

The Krug-M 2K11M version appeared in 1971, with an increase in the maximum range to 50 km, and a maximum range against low-altitude targets of 24.5 km.

Boost Propulsion: Solid rocket. Cruise Propulsion: Bondaryuk RD-058 Ramjet.

A further modernised version, the Krug-M1 2K11M1 began deployment in 1974. This could use an overtaking course to hit fleeing targets up to 20 km away, and reduced the minimum range to 6 to 7 km and reduced the maximum target altitude to 150 m.

Boost Propulsion: Solid rocket. Cruise Propulsion: Bondaryuk RD-058 Ramjet.

OAM MZIK developed the aerial targets Virazh and Virazh-M from the 3M8 and 3M8M missiles.

Manufacturer: OAM MZIK/Lyulev.

• Parsch, Andreas, DesignationSystems.Net, . Outstanding, unique reference for aircraft, missiles, propulsion, and avionics systems. Accessed at: http://www.designation-systems.net/.

• Yeftifyev, M D, Iz istorii sozdaniya zenito-raketnovo shchita rossii, Vuzovskaya kniga, Moscow, 2000. Comprehensive history of development of the development of surface-to-air and anti-ballistic missiles in the Soviet Union, with summaries of work in other countries as well. Accessed at: http://www.eastview.com/xq/ASP/sku=A2010232/f_locale=/Evtif'ev/MD/Moskva/Russia/Russian/qx/russian/books/product.asp.