Submarines of the US Navy - Page 2


The Trident missile, named after the trident, is an intercontinental ballistic missile (ICBM) which is armed with nuclear warheads and is launched from submarines (SSBNs), making it a SLBM.

The Trident was built in two variants: the I (C4) UGM-96A and II (D5) UGM-133A. The C4 and D5 designations put the missiles within the "family" that started in 1960 with Polaris (A1, A2 and A3) and continued with the 1971 Poseidon (C3).

Both Trident versions are three-stage, solid-propellant, inertially guided missiles whose range is increased by an aerospike, a telescoping outward extension that halves frontal drag.

The Trident is carried by fourteen active US Ohio class submarines and (with British warheads) four UK Vanguard class submarines.

The launch from the submarine occurs below the ocean surface. The missiles are ejected from their tubes by gas pressure created by a "gas generator", a solid-fuel rocket motor attached to the bottom of the missile tube which heats a pool of water creating steam. After the missile leaves the tube and rises through the water over the submarine, the first stage motor ignites, the aerospike extends, and the boost stage begins. Ideally, the missile is "sheathed" in gas bubbles for its entire time in the water, so liquid never touches its fuselage. Within about two minutes, after the third stage motor fires, the missile is traveling faster than 20,000 ft/s (6,000 m/s).

Trident I (C4) was deployed in 1979 and phased out in the 1990s and early 2000s. Trident II (D5) was deployed in 1990; it is planned to be in service past 2020. As of 2005, a decision is expected soon about whether or not to replace the UK's missiles and submarine fleet. Critics from the peace movement and within the military establishment have questioned the usefulness of such a weapon in the current military climate. The use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, according to an Advisory Opinion issued by the International Court of Justice in 1996.

Trident Missile Launch

Trident II (D5) UGM-133A

The second variant of the Trident is more sophisticated and can carry a heavier payload. It is accurate enough to be a first strike weapon. All three stages of the Trident II are made of graphite epoxy, making the missile much lighter. The Trident II was the original missile on the British Vanguard and later Ohio SSBNs.

Vanguard Class Submarine


The Royal Navy's Vanguard class of nuclear ballistic missile submarines (SSBNs), each armed with 16 Trident II SLBMs, includes four boats: Vanguard (S28), Victorious (S29), Vigilant (S30), and Vengeance (S31), all built by Vickers Shipbuilding and Engineering Ltd, now BAE Systems Submarines.


The Vanguard Class was designed from the outset as a nuclear powered ballistic missile submarine, unlike the previous Resolution class which was adapted from the then existing Valiant class SSN. At more than 150 metres long and 16,000 tons submerged displacement the Vanguards are roughly twice the size of the Resolutions, and are the third largest submarines ever built (after the Russian Typhoon and American Ohio classes). The great increase in size is largely related to much larger size of the Trident D-5 missile as compared to Polaris.

The Vanguards were designed and built at Barrow-in-Furness by Vickers Shipbuilding and Engineering Limited (VSEL). The Devonshire dock hall was built specifically to build these submarines. The missile compartment is based on the system used on the Ohio class, though only 16 missiles are carried rather than the 24 of the Ohio.

In addition to the missile tubes the Vanguard class is fitted with four 533 mm (21 inch) torpedo tubes and carries the Spearfish heavyweight torpedo, allowing it to engage submerged or surface targets at ranges up to 65 kilometres (40 miles). Two SSE Mark 10 launchers are also fitted to allow the boats to deploy Type 2066 and Type 2071 decoys, and a UAP Mark 3 electronic support measures (ESM) intercept system is fitted.

Vanguard, Victorious, Vigilant and Vengeance were commissioned in 1993, 1995, 1996 and 1999 respectively.


Vanguard carries the Thales Underwater Systems Type 2054 composite sonar. The Type 2054 is a multi-mode, multi-frequency system, which incorporates the 2046, 2043 and 2082 sonars. The fleet is in the process of having their sonars refitted to include open architecture processing using commercial off the shelf technology.

A Type 2043 hull-mounted active/passive search sonar is also carried, as is a Type 2082 passive intercept and ranging sonar. Finally a Type 2046 towed array is carried. This operates at very low frequency, giving a passive search capability.

Two periscopes are carried, a CK51 search model and a CH91 attack model. Both have a TV camera and thermal imager as well as conventional optics.

A Type 1007 I-band navigation radaris also carried.


A new pressurised water reactor, the PWR 2, was designed for the Vanguard class. This has double the service life of previous models, and it is estimated that a Vanguard class submarine could circumnavigate the world 40 times without refuelling. This should allow the class to carry out their entire service life without the need for expensive refuelling. The reactor drives two GEC turbines linked to a single shaft pump jet propulsor. This propulsion system gives the Vanguards a maximum submerged speed of 25 knots. There are two Paxman diesel alternators and two turbo generators from WH Allen.


The total acquisition costs of the Trident programme are 12.57 billion (at 1996-97 prices), which is over 3.6 billion lower in real terms than the original 1982 estimate. Government estimates put the cost of the entire Trident program at approximately 200 million per year over a 30 year in-service life. This estimate includes manpower, stores, refits, transport, shore facilities, decommissioning and disposal costs plus some of the expense of the Atomic Weapons Establishment.

UK nuclear policy

The principle of operation is based on maintaining deterrent effect by always having at least one submarine at sea, and was designed for the Cold War period. One submarine is normally undergoing maintenance and the remaining two in port or on training exercises. According to the Bulletin of the Atomic Scientists, UK SSBN patrols are co-ordinated with the French. They were "detargeted" in 1994 in time for their first maiden voyage.

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