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Copyright © 2002 Andreas Parsch

Boeing RUM/UUM-125 Sea Lance

In 1980, U.S. Congress approved the the U.S. Navy's ASW-SOW program, which was to provide a common successor to the UUM-44 Subroc submarine-launched and RUR-5 ASROC surface-launched anti-submarine missiles. The designations UUM-125A and RUM-125A were allocated to the projected submarine- and surface-launched variants, respectively. After designs by four different contactor teams had been evaluated, Boeing was awarded the prime contract for the ASW-SOW in 1982. The missile was subsequently named Sea Lance by the Navy (after Boeing had suggested Seahawk). However, it soon became apparent that the technical challenge of a combined development of both UUM and RUM versions would be too risky, and the RUM-125 was therefore deferred in 1983 (with the RUM-139 VL-Asroc developed as an interim weapon instead).

Boeing's UUM-125A Sea Lance design was to be launched from the submarine's standard 53.3 cm (21 in) torpedo tube inside a watertight canister, which would then float to the surface in a vertical attitude. On the surface, the missile's solid-rocket booster would ignite, and the Sea Lance's inertial guidance system would direct the missile toward the expected target position, using flip-out tail fins for stabilization. RUM-125A rounds would have been launched from a similar canister stored inside a MK 41 VLS (Vertical Launch System) cell. Targeting information was to be given to the missile before launch by the MK 117 digital fire control system. After motor burnout, the UUM-125A would coast on until, at a precalculated point of the flight path, the payload would separate from the rest of the missile. Before entry into the water, a parachute system would decelerate and stabilize the payload. The payload of the UUM-125A, as well as the RUM-125A, was planned to be a nuclear depth charge with a W-89 thermonuclear warhead. The W-89 was the warhead of the projected AGM-131A SRAM II with a nominal yield of 200 kT. For application in the UUM-125A, the yield would probably have been reduced. The very large lethal radius (about 10 km) of the warhead would have allowed usage of the missile to its maximum range of 185 km (100 nm) despite its inherent limited accuracy.

Drawing: U.S. Navy

At some time in the mid-1980s, a conventional alternative to the nuclear payload was proposed, too. This was to be the then new MK 50 torpedo, known as ALWT (Advanced Light-Weight Torpedo). The projected conventionally armed submarine- and surface-launched missiles were designated as UUM-125B and RUM-125B, respectively. Because of the limited search range of the torpedo, effective range of the RUM/UUM-125B would be reduced to about 65 km (35 nm).

Progress in the Sea Lance program was slow from the beginning, and it took until 1986, that Boeing was finally awarded a full-scale development contract. In 1988, it was again decided to develop the surface-launched RUM-125 in parallel, and it was planned to procure up to 3500 RUM/UUM-125B missiles (the nuclear-armed -125A had been indefinitely deferred at that time). However, this was not to be, because in 1990, the whole Sea Lance program was cancelled for budget reasons. It seems that no all-up RUM/UUM-125 missiles were ever test-flown.

In the early 1990s, parallel to the retirement of the UUM-44 Subroc, it was tried to restart the Sea Lance program, but to no avail. Therefore, U.S. Navy attack submarines currently have no high-speed loing-range stand-off weapon at their disposition.


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

Data for UUM-125B (except where noted):

Length6.25 m (20 ft 6 in)
Diameter53.3 cm (21 in) (encapsulated)
Weight1400 kg (3100 lb)
SpeedMach 1.5
Range185 km (100 nm); effective to about 65 km (35 nm)
PropulsionHercules EX 116 MOD 0 solid-fueled rocket
WarheadMK 50 homing torpedo
UUM-125A: W-89 thermonuclear (200 kT)

Main Sources

[1] Bernard Blake (ed.): "Jane's Weapon Systems 1987-88", Jane's, 1988
[2] Norman Polmar: "Ships and Aircraft of the US Fleet", 15th ed., Naval Institute Press, 1993

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Last Updated: 28 May 2002