One of Jeremy Corbyn's first battles shortly after he became Labour leader was trying to have a debate on the renewal of Trident, Britain's submarine-based nuclear deterrent. Introduced in 1994 to replace the predecessor system Polaris, Trident is expected to last until the middle of the next decade, which means that construction of a new system needs to begin soon. Jeremy Corbyn doesn't believe that it should be renewed, and the Conservatives have called a vote today on whether its replacement should go ahead. The Conservative have consistently pledged a replacement to Trident, promising four submarines to deliver a continuous deterrent with a submarine always at sea at a likely cost of over £20bn just to build. Given the immense cost - the nuclear fleet are the most expensive items the UK owns - why would the UK want to maintain the ability to launch nuclear missiles from beneath the sea?

In a 2007 vote, MPs voted for plans to renew Trident by 409 to 161. Since then the government has been spending hundreds of millions of pounds planning the Trident replacement. As one of the five permanent and founding members of the Security Council, the UK is one of the biggest global defence spenders and a recognized nuclear power with the power to veto UN Security Council resolutions. The UK hasn't used the right to veto since 1989 when it was used to defend the US invasion of Panama, but with that place on the UN Security Council the UK has a seat at the very highest table in international politics alongside the USA, Russia, China and France.

While some point to the difficulty of removing the UK from the Council, members are the only states recognized as "nuclear weapon states" under the Nuclear Non-Proliferation Treaty, and many fear that abandoning the UK's nuclear weapons would loosen our grip on permanent membership.

Since the US bombing of the Japanese cities of Hiroshima and Nagasaki in 1945, no nation has used a nuclear weapon in wartime. During the Cold War, the UK's nuclear submarines were part of NATO's targeted planning of USSR sites to allow NATO to launch a nuclear counter strike independent of national orders. Such drastic planning for the remote circumstances of a full-scale nuclear war were part of the stalemate that prevented the Cold War from ever becoming hot and prevented "nuclear blackmail" of Europe.

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Today, India and Pakistan's nuclear weapons are part of the fragile balancing act between the nations that has prevented full-scale war. With Russia's expansionist conduct in Georgia, the Ukraine, and their actions in Syria, it would be impossible not to rule out Russia as a threat to global peace and stability. The threat of nuclear weapons might not deter Isis, but between states they have the powerful effect of raising the stakes to a point at which conventional warfare becomes too dangerous to contemplate. As the victim of nuclear weapons, Japan has long avoided them, but with tensions with China in the East China Sea, there have even been calls in Japan to develop nuclear weapons. Given the global trend towards proliferation, unilateral abandonment of nuclear weapons is considered by many to pose a major risk to the UK's security.

Submarine-based nuclear weapons give the UK the ability to hide their nuclear weapons, and to fire them independent of communication. One of the first jobs an incoming UK prime minister has is to sit and write the instructions to nuclear submarines that sit in their safes while on patrol, to be opened in the event of nuclear war. These "letters of last resort" are part of the system that ensures the UK's nuclear deterrent is a functioning deterrent in all circumstances. At any one time the UK has a submarine carrying 16 nuclear missiles, each capable of hitting targets 7,000 miles away. Each missile has a dozen independent warheads with the power to destroy a city. There is no scenario in which the destruction of 192 cities is a good outcome, but the chilling effect of Trident is to massively discourage aggression against the UK or nuclear blackmail by states against the UK. There are even rumours that Margaret Thatcher persuaded French President François Mitterrand to give the UK the codes to disable Argentina's French missiles during the Falklands war by threatening to fire a nuclear weapon at Argentina. Such is the persuasive power of such weapons in conflict, even when they are not deployed.

Britain's nuclear deterrent is an expensive one, but it is estimated that up to 15,000 jobs depend on it. Britain has never had to use a nuclear weapon, but there is evidence that having them has assisted the UK in conflict and in peacetime. While the rest of the world continues to pursue them, it would seem prudent to hold on to ours, and to our foremost position in the United Nations. Jeremy Corbyn couldn't persuade his party even to debate Trident, let alone to vote against it, which will leave Britain's top military planners, and the British defence industry, sighing with relief.

Follow Rupert Myers on Twitter: @RupertMyers