A decision on where the axe will fall on the armed forces has been brought forward, the defence secretary said today.
Dr Liam Fox confirmed that an announcement following a major review of defence spending will be made in the last week of October.
The decision was previously expected to be released at Christmas.
Dr Fox said all sectors were being considered but no decisions had yet been made.
He said: "We have some difficult decisions but the crux decision is what are the risks we are willing to take for Britain's national security.
"We will make most of the difficult decisions in September, I will then take the sum of that to the national security council and make my announcement in the last week of October."
Dr Fox said a fixed budget had not yet been set by the Treasury and added that negotiations were "ongoing".
Last week, Chancellor George Osborne announced that the full £20 billion cost of renewing the UK's Trident nuclear deterrent must be paid for out of the defence budget.
Previously it had been funded directly by the Treasury.
When asked if he had been surprised by the announcement, Dr Fox said: "In politics nothing surprises me."
He added: "We are having ongoing discussions with the Treasury and we intend to continue those discussions.
"We have always said that we must maintain Britain's independent nuclear deterrent and the most cost effective way is replacing the naval missile programme.
"We have a value for money review reporting to the Treasury but we will have a continuous deterrent."
Dr Fox said he could not confirm whether major defence projects such as the two new aircraft carriers currently on order would survive the defence review.
He said: "We are still in the review, it is still ongoing, we do not know the size of the budget and the answers will be known in October."
He added: "A lot of the contracts that have been entered into will be as expensive to leave as to continue but we will want to make decisions about what is best for the defence in the long term."
Dr Fox made his comments during a visit to the Type 23 anti-submarine warfare frigate HMS Richmond carrying out navigation exercises off the Isle of Wight.
The minister arrived by Merlin helicopter and during the visit, he fired the ship's machine guns and took part in a demonstration on board one of the ship's sea boats.
The visit followed high level discussions at the Navy's headquarters on Whale Island, Portsmouth, Hampshire.
Captain Mike Wallacher, the ship's commanding officer, said he hoped to use the visit to show the versatility and importance of the role of a frigate to the Navy.
He said HMS Richmond had been involved in anti-piracy and anti-drugs operations, as well as protecting Iraq's oil fields and assisting in humanitarian missions in the Caribbean.
"The Navy is definitely busy, there's no doubt about it," he said.
"Whether it's stretched is a different matter.
"We are always working as hard as we possibly can and there's no doubt the Navy is being sweate