The UK currently has four Trident-armed Vanguard-class submarines, and the system is commonly described as costing about £205 billion over its full lifetime in one widely cited estimate, though other estimates vary.

Fleet size

The UK’s nuclear deterrent is based on four Vanguard-class ballistic missile submarines. One is usually on patrol, one or two can be ready at short notice, and one may be in maintenance.

Cost

A BBC explainer puts the Trident system’s replacement cost at about £205 billion when you include submarines, warheads, infrastructure, running costs, and decommissioning.

A few points matter here:

  • That figure is a lifetime estimate , not just the price of the submarines themselves.
  • The original submarine-build portion was estimated at £31 billion , with extra contingency and long-term operating costs making up most of the total.
  • Other reports and campaign groups have argued for different totals, so the exact figure depends on what is included.

Simple version

  • How many? Four Trident submarines.
  • How much? Roughly £205 billion across the full programme, according to one major estimate.

The key detail is that “Trident cost” usually means the whole nuclear deterrent system, not only the boats themselves.

TL;DR: the UK has 4 Trident submarines , and the deterrent is often estimated at around £205 billion in total lifetime cost.