Trident is also the name of the currently-modern family of U.S. Navy Fleet Ballistic Missiles (FBM), which are carried by (and launched from) nuclear ballistic missile submarines (SSBNs). The name is drawn from the mythical weapon of the god ofthe sea, Poseidon or Triton (for example) depending on which mythform you subscribe to.

The Trident comes in two 'flavors,' the C4 (Trident I) and the D5 (Trident II). They represent, in turn, the fifth and sixth generation of U.S. Navy FBMs since the program's inception with the Polaris system, which was first deployed in 1960. Ever since that time, the U.S. Navy has had missile submarines at sea as a deterrent - a secure, second-strike force able to 'ride out' any attack on the U.S. itself. The actual role of these missiles has become blurred as their capability has increased; the guidance system in the Trident missiles is reportedly on a par with that found in the Minuteman III ICBM. Coupled with advances in submarine navigation and positionfinding, this would mean that these weapons are accurate enough to be used for counterforce (first-strike) purposes.

Unlike the land-based missiles of the U.S. Air Force, the Navy's current crop utilize a dual-mode guidance system. The missile is guided during flight by an inertial navigation system; however, during post-boost, the trajectory and position are checked using a star tracker to perform a state vector update. As a result, Trident equipment sections have a small armored window to allow the astronavigation instruments to do their job.

For a better description of the operation and structure of submarine-launched missiles in general, see the writeup on SLBMs.

The Trident-class missiles are deployed by the U.S. solely on Ohio-class (SSBN-726) boats. Each boat carries 24 Tridents. The Trident series (both the C4 and the D5) is MIRV-capable, meaning each can carry up to five RVs, each able to carry a warhead. The C4 and D5 variants differ much more than their common name suggests; the D5 is really a new missile with system commonality to the C4. The D5 has a diameter of 83 inches compared to the C4's 74; this alone meant massive refits to Ohio's geared to carry the C4. In addition, the post-boost phase behavior of the D5 differs to improve accuracy, and the newer RVs on the D5 have been improved to better retain shape and thus aerodynamic stability during reentry.

The Trident weapon system was sold by the United States to Great Britain for use in its own SSBNs. The missiles, launching systems and fire control systems were all transferred. The U.K. built its own submarines and nuclear warheads to place on the missiles, and this system remains in service with the Royal Navy to this day, operated out of Faslane Scotland.

The good part - some stats. Woohoo! These are courtesy of the U.S. Navy's fact file, the Federation of American Scientists, and some Lockheed Missiles & Space propaganda.

Format: (stat) (C4 value) / (D5 value)

  • Unit Cost: --na-- / $30.9 million
  • Contractor: Lockheed Missiles & Space (both)
  • Propulsion: three-stage solid-fuelled rocket motor
  • Length: 10.2m (34 ft) / 13.41m (44 ft)
  • Diameter (Max): 1.8m (74 in.) / 2.11m (83 in.)
  • Weight at Launch: --na-- / 58,500 kg (130,000 lbs.)
  • Maximum Range: 4000 nm / "Greater than 4000 nm" (heh.)
  • Payload: (both) 1-5 Mk.4/5 RV w. nuclear warhead
  • Guidance: (both) Inertial with startracker verification midcourse
  • Year Deployed: 1979 / 1990