The UK government is to purchase 12 new fighter jets which can be equipped with nuclear bombs, and join Nato's airborne nuclear mission.
Downing Street says the move is "the biggest strengthening of the UK's nuclear posture in a generation".
The new F-35A jets can still carry conventional weapons, but have the option of being equipped with US-made nuclear bombs.
The decision will be announced by the prime minister at the Nato summit taking place this week in the Netherlands.
Nato's airborne nuclear mission involves allied aircraft being equipped with American B61 bombs stockpiled in Europe.