The missile was a two-stage development of the single-stage R-27, the second stage containing the warhead as well as propulsion and terminal guidance. Initial submarine testing began on 9 December 1972 on board the K-102, a project 605 class submarine, a modified Project 629/ NATO Golf class lengthened 17.1m (formerly B-121), to accommodate four launch tubes as well as the Rekord-2 fire control system, the Kasatka B-605 Target acquisition system and various improvements to the navigation and communications systems. Initial trials ended on 18 December 1972 because the Rekord-2 fire control system hadn't been delivered yet. After a number of delays caused by several malfunctions, test firings were finally carried out between 11 September and 4 December 1973. Following the initial trials, the K-102 continued making trial launches with both the R-27 and the R-27K, until it was accepted for service on 15 August 1975. Using external targeting data, the R-27K/SS-NX-13 would have been launched underwater to a range of between 350 and 400 nm (650–740 km), covering a "footprint" of 27 nm (50 km). The Maneuvering Re-Entry vehicle (MaRV) would then home in on the target with a CEP of . Warhead yield was between 0.5-1 Mt. The missile system never became operational, since every launch tube used for the R-27K counted as a strategic missile in the SALT agreement, and they were considered more important. Although the R-27K could fit in the launch tubes of the Project 667A (NATO Yankee class), the subs lacked the necessary equipment to target and fire the missile. Zyb (Suborbital Launch Vehicle) In 1992, there was an ongoing effort to convert surplus Soviet Navy SLBMs which were taken out of service into launch vehicles. The Zyb sounding rocket was created on the basis of the R-27 specifically for performing experiments in a Microgravity environment. The rocket would be launched in an ballistic arc, exposing the payload to weightlessness for 17 to 24 minutes, depending on payload mass. The trajectory would reach its apogee at 1800 km or 1000 km for 650 kg and 1000 kg payload mass respectively. The rocket provided 1.5m3 of payload volume. The Zyb sounding rocket was launched a total of three times. Derived missiles In 1992, the Makeyev Rocket Design Bureau signed a contract with North Korea regarding the creation of a R-27 derived launch vehicle. As a result of this, the very similar North Korean Hwasong-10 "Musudan" IRBM