Britain needs two aircraft carriers, not one, if it is to provide a credible answer to the global threat to maritime security, the head of the Royal Navy has said.
Admiral Sir George Zambellas, who is First Sea Lord and chief of the naval staff, said having two carriers ensuring continuous availability was "a modest extra premium to pay" for an "effective, credible, available, insurance policy".
His comments come just days before the navy's new aircraft carrier and biggest ever ship, the HMS Queen Elizabeth, is formally named by the Queen.
Admiral Zambellas was delivering the keynote speech at the Rusi (Royal United Services Institutes) International Sea Power Conference 2014 in Whitehall.
He said that the Queen Elizabeth class ships would deliver more than carrier strike for the British navy, but highlighted the importance of having two - not one.
"Credibility also hinges on a carrier being available when the need arises," he said. "Hope is not a reliable method of ensuring capability availability when a crisis erupts.
"That is why we need the effects of a UK carrier - it's the wrong moment to find out that nothing happens when you push the carrier button.
"So to ensure continuous carrier availability that means having two carriers, not one - a decision for government in next year's SDSR (Strategic Defence and Security Review) of course, but this is a modest extra premium to pay, for an effective, a credible, an available, insurance policy."
Admiral Zambellas' comments echo those made by former head of the Royal Navy Admiral Lord West of Spithead, who last month said that without an increase in defence spending, the nation was "on the road to disaster" and "balanced on a knife edge".
Lord West criticised plans for the near-completed second aircraft carrier HMS Prince of Wales, which suggested tying the latter up or selling it for a "bargain basement price".
He said: "This means that instead of our nation having a carrier available 100% of the time - and my goodness me in the next 50 years I promise you our country will need it, sadly we will - we will only have one available 80% of the time and of course in a national emergency we could have had two carriers.
"All my experience and I'm sure many of yours tells you when a national crisis arises it will be in that 20% of downtime. That is the way it goes."
HMS Queen Elizabeth will be formally named by the Queen on Friday, when she will smash a bottle of whisky against it at Rosyth in Fife, where the 65,000-tonne aircraft carrier has been assembled and fitted out.
The ship and a second vessel, the under-construction HMS Prince of Wales, are both termed Queen Elizabeth Class aircraft carriers and are the largest warships ever built for the Royal Navy. Assembly of HMS Prince of Wales is set to begin at Rosyth later this year.
Those behind the project, which costs an estimated £6.2 billion overall, say the QE Class will be the centrepiece of Britain's naval capability.