You don't realise it's there most of the time, but the UK could be a very different place without the existence of the Trident nuclear deterrent. Or at least that's what the Prime Minister is suggesting.
This is what we're talking about:
The Government is set to vote tonight on whether we should be renewing the deterrent, which consists of four Vanguard submarines - each carrying Trident missiles - which have been patrolling the oceans since 1969.
Making her first appearance in the Commons as Prime Minister, Theresa May has urged MPs to vote in favour of renewal, saying that threats from countries like Russia and North Korea "remain very real" and that we "need to be prepared to deter threats to our lives and our livelihoods and to those of generations who are yet to be born."
However, a number of Labour MPs are strongly against renewal, even suggesting that Trident should be removed altogether.
Assuring the room that, were he prime minister, he would not be prepared to order a nuclear strike on another country, Jeremy Corbyn said: "I do not believe the threat of mass murder is a legitimate way to go about dealing with international relations."
May, however, confirmed that she would be prepared to "push the button" on a strike if it were necessary to protect the country.