Zvezda Kh-66 (AS-7 Kerry)
Zvezda Kh-23 (AS-7 Kerry)

In April 1965, when work on the MiG-23 fighter aircraft began, the "Vympel" [Pennant] OKB-134 Special Design Bureau received an order for a Kh-23 tactical guided air-to-ground missile. The main incentive for developing it was intelligence received about the Bullpup missile, a highly effective American one of the same class built several years earlier. Right away the engineers faced an obstacle of technological nature: the Russians had never before built tactical guided missiles and had not acquired any experience with missile guidance systems. A particularly difficult problem was the stipulation by the Air Force that the missile guidance system fit already existing fighter aircraft and thus be small. Because the OKB-134 did not meet time schedules, the Air Force in early 1966 accepted the proposal from the "Zvezda" small Design Bureau at the Kalinin No 455 Series Production Plant near Moscow producing K-5, K-8, and other guided air-to-air missiles. They proposed to build the first tactical air-to-ground missile with ready-made components of air-to-air missiles.

What prompted the "Zvezda" OKB to submit its proposal was that it already had certain experience in using air-to-air missiles against ground targets. Such tests had been conducted during late nineteen fifties and early nineteen sixties with K-51 (RS-2US) missiles fired from MiG-19PM fighter aircraft. The main results of these tests indicated the feasibility of using these missiles against land and sea targets, though not very effectively because of the small warhead.

The first Soviet tactical air-to-ground missile was built in 1966 and, therefore, called the Kh-66 or Article 66. The key design requirement was that it be able to carry a warhead weighing 100 kg (for comparison, the warhead of the K-5 missile weighed 13 kg). For propulsion of the Kh-66 missile the propulsion system of the K-8 was used with only a small modification of the nozzle. The nozzle had to be split in two, because the K-51 (RS-2US) guidance system, also used by the Kh-66 missile, was located in the tail. Using the old guidance system had many drawbacks but also offered one great advantage, namely that it could be carried by every aircraft previously carrying a K-5 missile without modifications of the aircraft (except for a new attachment underneath the fuselage). The missile was produced within a few months and in September 1966 began to be tested with an MiG-21PFM aircraft. Then in 1968 the Kh-66 was officially certified as weapon of MiG-21 aircraft, supported on the center line beneath the fuselage.

The Kh-66 missile was a temporary solution and therefore, work on the Kh-23 missile was not discontinued but transferred from the "Vympel" OKB to the "Zvezda" OKB.

Many components of the Kh-66 missile were used for building the Kh-23 and only the tail carrying the Delta-R1M radio-command guidance system had to be altered. Furthermore, the propulsion fuel was replaced with one having a higher energy content. The first ten experimental Kh-23 units were tested in the beginning of 1968. Due to defects, factory testing continued till the end of 1969. The cause of perturbations in the missile guidance could not be determined for quite a long time. Eventually the cause was found to be the wrong location of the smoke tracker allowing it to interfere both thermally and mechanically with the antenna of the guidance system. This problem was solved by placing the tracker on the tail extension of the missile. The aircraft part of the Delta apparatus was installed either permanently on the aircraft (Delta N and Delta NM) or in containers (Delta NG or Delta NG2 systems). After completion of Government Qualification tests on MiG-23S and MiG-23B aircraft in autumn 1973, the Kh-23 missile was in 1974 officially certified as weapon with the Kh-23M (Article 68M) designation.