3 April 2024

The UK’s Trident launch failure: a cause for concern?

William Alberque

The 30 January 2024 failure of a sea-launch test from HMS Vanguard of the United Kingdom’s nuclear-armed submarine-launched ballistic-missile (SLBM) system, the Trident II D-5, grabbed headlines. As the second successive failure – following one in 2016 from HMS Vengeance – the test raised questions around the reliability of the UK’s continuous at sea deterrent. However, examining the complete test history of the missile system reveals a success rate that more accurately demonstrates its reliability.

Statistics matter 

Contrary to some reporting after the launch, the Trident II D-5 SLBM has so far proved to be a very reliable system, with 191 successful sea launches and only five failures since 21 March 1989 – a failure rate of 2.6%. Alongside sea testing, the Trident II D-5 was tested on land 19 times from January 1987–January 1989, recording three failures. This means the Trident II D-5 has been tested 215 times by the United States and the UK in total, including eight failures, five of which occurred between 1987–89. While two failed UK sea launches in a row is dispiriting, and the timing is embarrassing due to the presence of Secretary of State for Defence Grant Shapps and First Sea Lord Admiral Sir Ben Key on board the HMS Vanguard for the most-recent test, they do not necessarily indicate a shortcoming in the system.

The UK has only launched 12 Trident II D-5s from submarines since the Royal Navy acquired the missile in 1994. The missiles are drawn from a shared pool with the US, which carries out all missile-surety tests, and they are only launched by the UK during its Demonstration and Shakedown Operations (DASO) – a series of tests carried out by submarines upon their construction and first sea cruise, or upon completion of a period of maintenance. The UK’s first 10 launches succeeded, with each of the Vanguard-class submarines launching at least two Trident II D-5 missiles between 1994 and 2012 (see Figure 1). The two failures have both reportedly been attributed to human error. The failed test in 2016 was attributed to mis-programming the missile’s target coordinates, while the latest failure was reportedly due to modifications made to the missile in preparation for the test. The submarine and its crew were successfully certified following the most recent launch.

Track record 

The US, for its part, has launched the Trident II D-5 from submarines on 184 occasions, including only three failures – two in 1989 and one on an unspecified date in 2011 or 2012. US test launches are conducted both for certification of the missiles, including after the conclusion of life-extension programmes, and for US DASO operations. Throughout these tests, the Trident II D-5 has built up an exemplary record. In 2011, Lockheed Martin announced that the US and UK had launched the system successfully 135 times in a row from 4 December 1989–1 March 2011 – a notable rate of reliability for any system.

The first sea test of the Trident II D-5 missile on 21 March 1989 resulted in failure, leading to threats of cancellation from Congress as well as damage to the launching vessel, the USS Tennessee. The US then tested the missile successfully on 2 August 1989, before the third sea test resulted in another failure on 15 August that laid bare a fault in the design. Facing severe Congressional pressure, the US Navy needed to conduct a series of consecutive successful tests in order to certify the missile and to counter claims from Congress that the money would be better spent on conventional weapons. Seven consecutive successful tests between December 1989 and February 1990, culminating in a ‘ripple test’ of two missiles launched sequentially from the USS Tennessee on 12 February, lead to the system’s certification and full operational deployment in March 1990.

A careful examination of Lockheed Martin and US Navy press releases indicate that the next unsuccessful test occurred between 2011 and 2012. On 1 March 2011, the company announced the 135th consecutive successful test flight of the missile, before recording the 137th successful test flight on 22 February 2012. No subsequent announcements from the US Navy or Lockheed Martin list ‘consecutive’ successes, instead giving the total number of successful flights. The number of successful flights therefore increased to 137 with the 22 February test, which includes the non-sequential successful sea test on 2 August 1989.

The most recent US test of the Trident II D-5 took place on 27 September 2023; this marked the 191st successful sea launch since 1989 and resulted in a rate of four to five successful tests per year since 2012. However, this number also includes the 10 successful UK test launches since 1994. (This is demonstrated by earlier press releases in which the UK number is included in the total number of successful consecutive launches.)

Overall, the US has carried out 181 successful sea launches, which together with three failures gives a 1.6% total failure rate for US sea launches of the Trident II D-5. The failure rate of US land and sea launches together stands at 3%, and all six failures occurred before 1990. This is a remarkable success rate. While the UK’s recent sea-launch test failures give some cause to doubt the country’s testing and evaluation procedures, they give no reason to doubt the effectiveness of its nuclear arsenal.

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