The Royal Navy's Swiftsure class of nuclear fleet submarines (SSN) until December 2010, was the oldest of the three classes of fleet submarine in service with the RN.
Six boats were built and commissioned. HMS Swiftsure was decommissioned in 1992 due to damage suffered to her pressure hull during trials. HMS Splendid followed in 2004 after defence cuts caused a reduction in the size of the RN SSN fleet. HMS Spartan was decommissioned in January 2006, with HMS Sovereign following on 12 September 2006. HMS Superb was decommissioned on 26 September 2008. The remaining boat in the class, HMS Sceptre,was decommissioned in December 2010. They are being replaced by the Astute-class submarine.
A few were upgraded to be able to use Tomahawk missiles in addition to their original armaments of torpedoes, mines and anti-ship missiles.
The Dreadnought, Valiant and Improved-Valiant classes all had a "whale-shaped hull", of "near-perfect streamlining giving maximum underwater efficiency". The hulls were of British design, "based on the pioneering work of the US Navy in Skipjack and Albacore." The hull of the Swiftsure was a different shape and maintained its diameter for a much greater length than previous classes. Compared with the Valiants the Swiftsures were 13 feet "shorter with a fuller form, with the fore-planes set further forward, with one less torpedo tube and with a deeper diving depth."
A second major change was in propulsion. Rather than the seven/nine-bladed propeller used by the previous classes, all but the first of the Swiftsure-class submarines used a shrouded pump-jet propulsor. The prototype propulsor had powered the Churchill. It is not clear why the Swiftsure was the only one of the class not fitted with a propulsor. The propulsor was perhaps as much as 50% more efficient than a propeller, producing the same speed at lower revolutions, thus reducing the noise signature. In addition all pipework connections to equipment on the main machinery raft had expansion/flexible coupling connections, which also reduced noise. The US Navy secured a licence to copy the main shaft flexible coupling arrangement in US-built submarines.
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