In addition to a longer-range missile, a larger submarine was proposed to replace the Lafayette, James Madison and Benjamin Franklin-class SSBNs in 1978.

The ULMS II missile system was designed to be retrofitted to the existing SSBNs, while also being fitted to the proposed Ohio-class submarine.

The first test of the Trident was on January 18, 1977 when an unarmed missile was launched from Cape Canaveral in Florida and traveled almost its full range of 4,600 miles (7,400 km), to a point in the South Atlantic Ocean near Ascension Island.

Trident II (designated D5) had the objective of improved circular error probable (CEP), or accuracy, and was first deployed in 1990, and was planned to be in service for the thirty-year life of the submarines, until 2027.

[5] British Prime Minister Margaret Thatcher wrote to President Carter on 10 July 1980, to request that he approve supply of Trident I missiles.

[6] Under the agreement, the United Kingdom paid an additional 5% of their total procurement cost of $2.5 billion to the US government as a research and development contribution.

The subsequent pressure spike is strong enough to eject the missile out of the tube and give it enough momentum to reach and clear the surface of the water.

Once the star-sighting has been completed, the "bus" section of the missile maneuvers to achieve the various velocity vectors that will send the deployed multiple independent reentry vehicles to their individual targets.

This is the second failure in a row for the Royal Navy after a launch from HMS Vengeance, one of Britain's four nuclear-armed submarines, off the coast of Florida in June 2016.

The main aim is to replace obsolete components at minimal cost[citation needed] by using commercial off the shelf (COTS) hardware; all the while maintaining the demonstrated performance of the existing Trident II missiles.

In 2007, Lockheed Martin was awarded a total of $848 million in contracts to perform this and related work, which also includes upgrading the missiles' reentry systems.

[15] Then-British Prime Minister Tony Blair outlined plans in Parliament on 4 December 2006 to build a new generation of submarines (Dreadnought-class) to carry existing Trident missiles, and join the D5LE project to refurbish them.

[16] The first flight test of a D-5 LE subsystem, the MK 6 Mod 1 guidance system, in Demonstration and Shakedown Operation (DASO)-23,[17] took place on USS Tennessee on 22 February 2012.

US Navy Vice Admiral Johnny Wolfe, in charge of overall submarine weapons systems procurement, indicated in 2020 that he had initiated trade studies to apply lessons from the D5LE program to extend the Trident II's lifespan to 2084.