ASROC

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An older "Matchbox" ASROC launcher, phased out in the 1990s

ASROC (for Anti-Submarine ROCket) is an urgent-attack, all-weather, all sea-conditions anti-submarine missile system, developed by the United States Navy, and installed on over 200 surface ships, generally cruisers and destroyers. A surface ship, patrol plane or anti-submarine helicopter first detects an enemy submarine by using sonar, relaying the range and bearing information to the attacking ship who then fires an ASROC missile on an unguided ballistic trajectory, carrying an acoustic homing torpedo or Nuclear Depth Bomb (NDB) toward the target. At a pre-determined position on the missile's trajectory the payload separates from the missile and deploys a parachute to slow the torpedo or NDB to permit splashdown and water entry at a low speed and minimum detectable noise. Water entry activates the torpedo, and guided by its own sonar system it homes in on the target and explodes. When the missile carries a nuclear weapon, the unguided NDB, sinks quickly to a predetermined depth and detonates. An ASROC missile can carry a 10 kiloton W44 nuclear warhead, although the W44-based NDBs were retired by 1989.[2] See Ikara for a fuller explanation of the tactical rationale for these 'rocket-thrown' weapons.

The first ASROC system (RUR-5), using the MK-112 "Matchbox" launcher, was developed in the 1950s and installed in the 1960s. This system was phased out in the 1990s and replaced with the RUM-139 Vertical Launch ASROC, or "VLA".

Launch of a Vertical Launch ASROC

The VLA missile is a rocket-propelled, three-stage, anti-submarine warfare (ASW) weapon designed for deployment on Ticonderoga-class cruisers, Arleigh Burke-class destroyers, and Spruance-class destroyers equipped with the MK41 Vertical Launching System (VLS) and MK 116 fire control system. The VLA missile provides the fleet with the capability for rapid response, all weather delivery of a MK 46 torpedo against threat submarines in any direction at intermediate ranges. VLA missiles were introduced into the fleet in 1993 as a baseline weapon for the cruisers and destroyers equipped with the Aegis combat system and as a replacement for the ASROC weapon on Spruance-class destroyers when the original ASROC launchers were replaced by the MK 41 VLS.

VLA missiles were first introduced with the MK 46 torpedo as its payload (RUM139A). In 1996 an upgrade was implemented to allow the enhanced shallow-water capable MK 46 to be incorporated as the VLA missile payload (RUM139B). VLA missiles are delivered to the fleet as All-Up-Rounds (AURs) which consist of the VLA missile installed inside of a MK15 VLS canister. VLA missiles have two basic fleet configurations, Warshot and Exercise. VLA Warshot missiles contain a MK46 warshot torpedo. VLA Exercise missiles contain an exercise torpedo, and are used for fleet exercise firings.

Primary Function: Surface Launched Missile, Anti-Submarine Warfare Weapon.
Contractor: Lockheed Martin, Naval Electronics & Surveillance Systems of Akron, Ohio (formerly Loral Defense Systems, formerly Goodyear Aerospace).

ASROC mission sequence. The range shown was typical of early ASROC rounds, before introduction of the VLA system with slightly extended range.[1]

Unit cost: Approximately $350,000 (less torpedo payload).
Power plant: Solid propellant rocket motor.
Length:
- Warshot: 16 ft 0.6 in (4.892 m)
- Exercise: 16 ft 8 in (5.08 m)
Weight:
- Warshot: 1407 lb (638 kg)
- Exercise: 1377 lb (615 kg)
Diameter: 16.6 in (422 mm)
Wing Span: 26 7/8 in (683 mm)
Range: 28 km (15 nm)
Guidance system: Inertial Guidance
Warhead: Mark 46 torpedo, 100 lb (45 kg) of PBXN-103 high explosive
Date Deployed: 1993 (RUM139A); 1996 (RUM139B)

ASROC worst-case miss distance when attacking a submarine travelling at 25 knots with the RUR-5 ASROC and Mk.44 torpedo combination. Attempting to splash the torpedo within acquisition-range of the torpedo acoustic seeker was entirely dependent upon a prediction of the submarine's movements. An astute submarine captain would take immediate and unpredictable evasive measures when hearing the ship's sonar echo. Only if the submarine maintained its approximate course and speed could the acoustic seeker be certain to lock-on to the target, and even then, a kill was not assured, especially if the missile's margin of error placed the torpedo astern of the submarine.