SA-X-21 Mysk

In 1996 there were reports that US sources had suggested the fact of the existence of a new Russian SAM system in development, with the US designators SA-X-21 and the Russian system nomenclature believed to be Mysk. However, no additional information was forthcoming for many years concerning either a Russian system designated Mysk, or any other system that might be associated with the SA-X-21 designator. One source suggested that the Mysk was a proposed development of SA-N-12 GRIZZLY, possibly with Terminal Active Radar Homing [TARH] seeker, and increased agility.

As of 1999 the Ballistic Missile Defense Simulation Support Center's Extended Air Defense Simulation [EADSIM] modeling database contained an entry for the SA-21, though publicly available details were lacking. The Extended Air Defense Simulation is a system-level simulation used to assess the effectiveness of Theater Missile Defense (TMD) and air defense systems against the full spectrum of extended air defense threats. EADSIM models performance and predicts effectiveness of ballistic missiles, surface-to-air missiles, aircraft missiles, and cruise missiles in a variety of user defined scenarios.

EADSIM was being used by all four U.S. military services, individually and jointly, at over 300 subscriber sites around the world. It is also being used by the United Kingdom, Israel, Australia, and the SHAPE Technical Center under Memoranda of Agreement with the U.S. Army. EADSIM has been used in support of the TMD Advanced Warfare Experiment, as well as TMD Cost and Operational Effectiveness Analysis studies. EADSIM was used successfully by the U.S. Air Force Studies and Analyses Agency to analyze attrition, Suppression of Enemy Air Defense missions, and refueling operations during Desert Shield and Desert Storm.

As of 2000 there were reports that the SA-21 designation referenced the S-500 complex, a new anti-aircraft, anti-missile system design by Almaz in competitive development with Antey's S-400 to produce a Russian equivalent to THAAD.

By 2007, it was apparent that the SA-21 NATO nomenclature was associated with the S-400 Triumf, with the NATO reporting name of GROWLER.