Labour and the Conservatives have become locked in a vicious fight today over the future of Britain's Trident nuclear deterrent.
Defence secretary Michael Fallon kicked off the debate with a scathing article in The Times where he accused Labour of using Trident as a "bargaining chip" for a possible deal with the SNP after the General Election.
Labour shot back with shadow foreign secretary Douglas Alexander lambasting Fallon's remarks as "desperate stuff from a rattled campaign".
At a press conference this morning Miliband reiterated his party's commitment to renewing Trident.
Earlier this month shadow chancellor Ed Balls suggested Labour would consider cutting the number of nuclear submarines as part of a strategic defence review. However, the debate rages on, so here's a cheat's guide to making sense of Trident.
What is Trident?
Trident is the UK's sea-based nuclear weapons system, including submarines, missiles and warheads, that was introduced in the 1990s.
Why does Trident need to be replaced?
The way the UK's Vanguard submarines were designed means that the nuclear propulsion system and the electric cables inside have a limited life span. If it is to be replaced, it will have to happen soon as the submarines can take up to 17 years to build.
How many nuclear subs are there?
The UK has four Vanguard submarines. Only one is armed and at sea, two are in port and the last is undergoing maintenance.
What weaponry does Trident have?
Each submarine carries 16 missiles and 48 warheads with a crew of 135 on board.
What does it cost?
According to the House of Commons library, the cost of replacing the Trident system could cost between £17.5bn and £23.4bn. However, the Campaign for Nuclear Disarmament claim Trident costs £100bn over its whole lifetime.
Where is it based?
Trident's principle base is in the west of Scotland with a submarine berth at Faslane and an ordnance depot at RNAD Coulport in Argyll.
Will it be replaced?
It is close to certain the Trident will be replaced. When it came up for a vote in parliament in 2007, for replacement carried the day 409 votes to 61. Both the Conservatives and Labour have promised to replace the system.
Who is opposed to Trident?
The SNP are the most powerful opponents of Trident and according to the polls, the SNP could hold the balance of power in a hung parliament.
The party's leader Nicola Sturgeon has said the removal of nuclear weapons from Scotland will be a red line in any future negotiations with Westminster. The Greens and Plaid Cymru stand with the SNP in opposing Trident.