But some in the defence world believe the whole debate is deluded. Trident, in its current form, was designed to deliver “minimum deterrence” – that is, using as little force as possible to threaten Russia with “unacceptable loss”. The method is to maintain at least one submarine continually at sea, armed with up to 12 missiles, each capable of dropping eight warheads on to enemy cities.
But few people understand that the UK’s nuclear deterrent is a system – not a technology – and one that must constantly evolve as the threat changes.
For a nuclear-armed submarine to pose a credible threat, it must avoid being tracked by Russian submarines. To do that it must get out of the River Clyde and, once at sea, be protected by aircraft trying to spot the Russian subs, plus an undersea surveillance system whose sensors are scattered across the ocean bed. On top of that, those controlling Trident must engage in a data-crunching battle with the Russian navy, whereby each side uses predictive modelling to guess where the other’s subs will be.
For informed critics and supporters of Trident, the difficulties start here. In 2010, David Cameron cancelled a programme to upgrade the Nimrod surveillance aircraft tasked to look for the Russian subs. The UK’s are now protected only by helicopters and ships.