UGM-73 Poseidon
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| Type | Strategic SLBM |
|---|---|
| Range | With MIRV: 2,500 nm, With RV: 3,200 nm |
| Warheads | 10 or 14 W-68 warheads of approx 50 kt yield in Mark 3 MIRVed RVs. 500 kt total |
| Propulsion | Two-stage solid-propellant rocket, each single nozzle with thrust-vectoring |
| Guidance system | Inertial |
| CEP | 0.3 nm (550 m) |
| Max speed | >8000 mph (12900 km/h) |
| Length | 34 feet 1.2 inches (10.39 m) |
| Diameter | 74 inches (1.88 m) |
| Weight | 64400 pounds |
| Manufacturer | Lockheed Martin Space Systems |
| In service | 31 March 1971 |
| Decommissioned | September 1992 (Trident I phased in from October 1979) |
| States | United States |
The Poseidon missile was the second US Navy ballistic missile system, powered by a two-stage solid fuel rocket. It succeeded the Polaris missile beginning in 1972, bringing major advances in warheads and accuracy. It was followed by Trident I in 1979, and Trident II in 1990.
A development study for a longer range version of the Polaris missile achieved by enlarging it to the maximum possible size allowed by existing launch tubes started in 1963. Tests had already shown that Polaris missiles could be operated without problems in launch tubes which had their fibreglass liners and locating rings removed.
The project was given the title Polaris B3 in November, but the missile was eventually named Poseidon C3 to emphasis the technical advances over its predecessor. The C3 was the only version of the missile produced, and it was also given the designation UGM-73A. [1]
Poseidon, although slightly longer and considerably wider and heavier than Polaris A3, had the same 4600 km (2500 nautical mile) range, although with increased payload weight. It also had improved accuracy and up to fourteen W68 thermonuclear warheads [citation needed] contained in Mk.3 RVs that were of a new MIRVed high-re-entry-speed design intended to counter sprint-type terminal ABM defences. See Atmospheric re-entry for blunt body theory.
The low-yield warheads were apparently selected to make the weapon unsuitable as a first-strike weapon against hardened targets in the Soviet Union,[citation needed] but could be used in a retaliatory strike against soft targets, or in a pre-emptive strike against unhardened surface targets such as airfields, SAM sites, radar sites and other similar targets, opening a pathway for heavy bombers. In later years this targeting technique has been demonstrated by the use of cruise missiles to neutralise airfields, SAM sites etc in the opening phases of the Gulf War. Similarly a new more accurate celestial/intertial guidance system was not developed because it was felt[citation needed] a highly accurate invulnerable weapon might destabilize the nuclear deterrence balance with the Soviet Union.[2]
As with Polaris, starting a rocket motor when the missile was still in the submarine was considered very dangerous. The missile was ejected from its launch tube using high pressure steam produced by a solid-fueled boiler.
The first test launch took place on 16 August 1968 whilst the first test launch from a submarine took place on the USS James Madison on 3 August 1970. The weapon officially entered service on 31 March 1971. It eventually equipped all 31 Layfayette-class submarines, the submarines' original Polaris outfit being replaced with Poseiden during refits.
About 620 UGM-73A missiles were built between 1970 and 1978.[3]
