Parliament will vote on plans to upgrade the nuclear Trident fleet on July 18, David Cameron has announced at a NATO summit in Poland.
"We must also invest in the ultimate insurance policy of all, our nuclear deterrent," he told a press conference as he discussed the UK's defence spending commitments.
The renewal of Trident has proved controversial. The Labour leader Jeremy Corbyn does not support the renewal of the nuclear fleet though other members pf his party do back the upgrade.
A renewal will cost billions and some argue it is a waste for a deadly weapon that is unlikely to be used. Others say its existence a vital deterrent against attack.
Mr Cameron defended his decision to call the vote himself instead of leaving it to a successor who will be appointed within months.
He said he wanted to hold the vote to put the renewal "beyond doubt" so military leaders could begin planning and spending decisions could be taken.