Lockheed Martin (Loral) RUM-139 VL-Asroc

In the early 1980s, the U.S. Navy sought to replace the surface-launched RUR-5 ASROC and the submarine-launched UUM-44 Subroc with a single new missile, the planned RUM/UUM-125 Sea Lance ASW-SOW (Anti-Submarine Warfare Stand-Off Weapon). However, the Sea Lance program encountered technical and funding diffulties, and it was decided that only the submarine-launched version (UUM-125A) would be initially developed. As an interim ASW weapon for surface ships, a simple derivative of the ASROC, compatible with the modern MK 41 VLS (Vertical Launch System), was to be created. A full-scale development contract for this missile, designated as RUM-139A VL-Asroc (Vertical Launch ASROC), was issued to Goodyear in 1983. Goodyear Aerospace was later acquired by Loral, whose defense division was purchased in 1996 by Lockheed Martin. A series of test firings took place in 1986, and it was planned to have the VL-Asroc operational by 1989. However, the program was halted in 1988, when it was again decided to develop a surface-launched version of the Sea Lance (RUM-125A) as well. The VL-Asroc program remained on hold until 1990, when the whole Sea Lance program was cancelled. As if matters were not confusing enough, it was briefly tried to reactivate the Sea Lance in the early 1990s, but without affecting the status of VL-Asroc as primary surface-launched anti-submarine weapon. The RUM-139A finally became operational with U.S. Navy ships in 1993, and more than 450 missiles have been procured so far.

The RUM-139A is an RUR-5 ASROC rocket with a completely new solid-rocket booster section, for launch from the MK 41 VLS of modern U.S. Navy surface combat ships. In addition to the ASROC's inertial guidance system, the VL-Asroc uses a digital autopilot, which controls the flight path using the thrust-vector control of the MK 114 MOD 0 solid-rocket booster. The autopilot makes the RUM-139 more manoeuverable than the RUR-5, and enables it to fly a shallower trajectory, avoiding errors by high-altitude winds. The range is controlled as in the RUR-5, i.e. by motor cutoff and airframe separation at a precalculated point in the trajectory. The payload of the RUM-139A is a MK 46 MOD 5A light-weight homing torpedo, which is decelerated and stabilized by a parachute system before it enters the water. It was originally planned to create also an RUM-139 variant with the MK 50 torpedo, but this was cancelled. The RTM-139A is a training version with an inert exercise torpedo, and the DRUM-139A is a non-flying dummy missile for ground training in a laboratory environment (the DRUM prefix is slightly off-standard, it should have been DRTM instead).

Photo: U.S. Navy Photo: Lockheed Martin RUM-139A

Around 1995, the manufacturer of the MK 46 MOD 5A torpedo (then Honeywell/Alliant, today Raytheon), developed a variant with enhanced shallow-water capability, known as MK 46 MOD 5A(SW). Beginning in 1996, U.S. Navy RUM-139A missiles were retrofitted with the upgraded torpedo, and designated RUM-139B. By 2001, all RUM-139As had been upgraded to this standard. The RTM-139B uses an inert variant of the MK 46 MOD 5A(SW).

The designation RUM-139C was allocated in 2001 to a VL-Asroc variant carrying the Raytheon MK 54 MOD 0 torpedo, also known as LHT (Lightweight Hybrid Torpedo). The MK 54 is a new lightweight torpedo, which entered full-rate production in October 2004. Integration test and development of the new torpedo with the VL-Asroc will continue through 2005. As with the RUM-139A and B versions, there will also be an RTM-139C inert training variant of the RUM-139C.

Specifications

Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!

Data for RUM-139A/B (except where noted):

Length 4.89 m (16 ft 0.6 in) Finspan 69.6 cm (27.4 in) Diameter 35.8 cm (14.1 in) Weight 630 kg (1400 lb) Speed Mach 1 Range 28 km (15 nm) Propulsion MK 114 MOD 0 solid-fuel rocket motor Warhead MK 46 MOD 5A (-139A) or MOD 5A(SW) (-139B) torpedo (44 kg (98 lb) HE)

RUM-139C: MK 54 MOD 0 torpedo

Main Sources

[1] Norman Friedman: "World Naval Weapons Systems, 1997/98", Naval Institute Press, 1997

[2] Norman Polmar: "Ships and Aircraft of the US Fleet", 15th ed., Naval Institute Press, 1993

[3] Hajime Ozu: "Missile 2000 - Reference Guide to World Missile Systems", Shinkigensha, 2000

[4] US Navy Fact File: VLA Missile

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Last Updated: 6 December 2004