Four things to note about the Trident nuclear deterrent - and why the missile malfunction matters

Off the coast of Florida, a UK Trident missile misfired and crashed into the ocean.

An unarmed Trident II (D5) ballistic missile firing from HMS Vigilant at an unknown date. Pic: PA

It’s caused waves in the UK, while the government insists it was an “anomaly” that doesn’t compromise the country’s nuclear deterrent.

But what does a nuclear deterrent even mean, what is Trident – and why does the misfiring matter?

Sky News draws on the expertise of defence analyst Simon Diggins to bring you what you need to know.

What is Trident – and how is it a deterrent?

The Trident missile system is what is known as a continuous at-sea deterrent.

The UK has four nuclear-armed submarines, and one of these is always in the ocean to deter nuclear attacks.

It is intended to deter the most serious threats: “You’re talking about somebody who might threaten us with nuclear annihilation that would destroy our way of life,” Diggins explains.

It’s a “psychological weapon”, he adds: “The idea is, you do that to us, we’ve got something that we could do back to you.”

That “balance of terror” hopefully stops anyone from resorting to nuclear warfare.

The four submarines are armed with Trident missiles. They can carry 16 missiles – all of which can go to different targets – and each missile has 12 warheads, or nuclear bombs.

That means each boat could theoretically carry 192 warheads, but it is government policy to deploy no more than 40.

Each warhead is seven times as destructive as the bomb that destroyed Hiroshima.

How much does Trident cost – and is it value for money?

That’s a hard question to answer, Diggins says, because a lot of the costs are obscured – in part for security reasons.

The Campaign for Nuclear Disarmament (CND) estimated the cost of maintaining and replacing Trident over its lifetime would be £205bn – although that comes with the caveat that they hold an anti-nuclear position.

In 2016, then chair of the foreign affairs committee Crispin Blunt estimated the lifetime cost of renewing and running Trident to be £179bn.

According to a 2023 House of Commons briefing, replacing the current four submarines is expected to cost £31bn, with an extra £10bn set aside for contingencies.

The government acquired Trident in the 1980s at a cost of £12.5bn – about £21bn in 2022/23 prices.

The briefing says annual running costs are estimated at 6% of the defence budget – about £3bn for 2023-24.

But Diggins says the actual amount spent on Trident “could be larger, it could be up to a quarter of our total defence budget – but it’s hidden”.

Whatever the exact dollar cost, it’s a “major chunk out of our defence budget”, Diggins says.

“That leads to the biggest question – is it actually good value for money?”

In Diggins’ view, the answer is no.

“I’d be putting my money into ensuring that with the forces we’ve got, they have the resources in place, both people and equipment, to do the job they need to do now.

“Do we need [Trident]? There are enough mad bad people around in the world to justify it. But it should never be at the expense of effective conventional defence. And it is at the moment.”

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What went wrong in this test – and how often does that happen?

A Trident missile misfired and crashed into the ocean off the coast of Florida during a rare test launch involving HMS Vanguard.

According to The Sun newspaper, which first broke the story, the Trident 2 missile was propelled successfully from under the water into the air by compressed gas in the launch tube.

But its first-stage boosters did not ignite, and the 60-tonne missile – fitted with dummy warheads – splashed into the Atlantic Ocean and sank.

The fault is said to have had something to do with it being a test-firing, with a source saying the launch would have been successful had it been carried out for real with a nuclear warhead.

The Ministry of Defence called it an “anomaly”. But it is not the first time a test has ended badly.

The Royal Navy last test-fired an unarmed Trident II D5 ballistic missile in 2016 – and it flew in the wrong direction.

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What does the misfiring mean for UK defence?

The misfiring should be seen against the backdrop of other military failures, Diggins says.

The HMS Queen Elizabeth was supposed to be the centrepiece of the UK Navy’s contribution to the largest NATO exercise since the Cold War – but was forced to pull out of the mission because of a propeller “issue”.

It was replaced by the HMS Prince of Wales – which in 2022 broke down shortly after setting sail on what had been billed as a “landmark mission” to the United States.

Diggins uses the metaphor of Formula One engineering. What the armed forces have are a few bits of “incredibly sophisticated, very complicated” equipment – but it needs the robust, resilient stuff to back it up, he says.

The test failure came as Dmitry Medvedev – a former Russian president, senior Kremlin official and close ally of Vladimir Putin – threatened to use nuclear weapons against the US, UK, Germany, and Ukraine if Moscow loses all occupied Ukrainian territories. Mr Medvedev, it should be said, is infamous for such dire threats.

It is all posturing, Diggins says. But in the UK’s case, the posturing went “plop” in the ocean.

It’s a “PR disaster”, he says.

The Ministry of Defence has insisted Trident “remains safe, secure and effective”.

In a statement, Defence Secretary Grant Shapps confirmed “an anomaly did occur” – but stressed this was “event specific”.

“Nor are there any implications for our ability to fire our nuclear weapons, should the circumstances arise in which we need to do so,” he said.

Mr Shapps said the government has “absolute confidence” in the UK’s nuclear deterrent – and there are “no implications for the reliability of the wider Trident missile systems and stockpiles”.

He went on to warn: “The UK’s resolve and capability to use its nuclear weapons, should we ever need to do so, remains beyond doubt.”