During the 1990s reports intermittently emerged on Russian websites that an optical correlator based seeker was being developed for the SS-N-6 Serb for use as an ASBM, and that the technology had been sold to China. These claims were never confirmed.

Reports that the PLA was developing ASBM technology started appearing some years ago, but the existence of this weapon was not confirmed until recently.

Most sources agree that the Chinese ASBM is based upon a terminally guided variant of the DF-21 / CSS-5, which is a 1,000 nautical mile range class IRBM derived from the JL-1 series solid rocket propelled SLBM carried by PLA-N SLBMs. The DF-21 is carried by a towed TEL and is highly mobile, an ASBM variant would likely be deployed in exactly the same fashion, as mobile TELs are extremely difficult to locate and target prior to missile launch. There does not appear to be a strong consensus in open sources on whether the DF-21 SLBM uses a radar or an optical seeker. There is a strong consensus that the DF-21 SLBM is intended as an anti-access weapon, to keep US Navy carrier battle groups outside China’s first and second island chains.

The DF-21 IRBM is a difficult missile to stop using a tactical or theatre ABM system due to its high re-entry velocity, as it sits at the outer performance envelope of contemporary ATBM systems. A bigger concern is that DF-21 ASBMs could be salvoed to produce multiple round saturation attacks against naval task forces. There will be practical limits to how many concurrent engagements against ASBMs can be handled by a single ABM system such as the SPY-1 Aegis. The high re-entry velocity of such targets demands a high update rate during tracking, and this in turn consumes per target some share of the total tracking time available from each Aegis system. There will be, as with supersonic ASCMs, some hard limit beyond which these systems are overwhelmed.

While existing warship defensive systems with ABM capability will have no difficulty in engaging small numbers of such weapons, saturation attacks change the whole strategic dynamic. Compared to ASCM attacks, ASBM attacks offer more warning time as the ionization trail of the MARV is readily detected by radar. On the other hand, ASBMs are significantly faster making them more challenging targets to intercept. While ASCMs can still be engaged by close in gun systems or lasers once inside the minimal engagement distance of defensive missiles, ASBMs are much too difficult a target for such terminal defences – their speed alone requires exceptionally high tracking rate performance for an effective intercept. From a lethality perspective, even an ASBM armed with an inert concrete warhead presents as a highly lethal projectile, given the exceptional terminal velocity at impact. The kinetic energy at impact of a single ASBM MARV is roughly 10 to 20 times greater than that of a concrete piercing guided bomb.

While opportunities may exist to jam a RADAC style seeker, the propensity to combine passive anti-radiation homing seeker technology into existing ASCM active radar seekers make this a marginally viable strategy in the long term. The cost of an ASBM and its targets make the installation of sophisticated multi-mode seekers entirely justifiable.

It therefore comes as no surprise that China’s deployment of the DF-21 ASBM has produced a very loud public debate in the United States. Anti-shipping weapons technology and shipboard defences have been locked into an evolutionary

arms race for two millennia now, and the latest cycle is currently favouring the attacker. How soon credible defensive technologies can be deployed remains to be seen.

http://www.ausairpower.net/SP/DT-ASBM-Dec-2009.pdf