The Times today reported that the First Sea Lord, Admiral Sir George Zambellas, said the navy faced ‘the fight of our generation’ to stay credible.

He wants to keep a mix of warships, submarines, fighter jets and Royal Marine boats and aircraft, the national newspaper said.

The Times reported that in a private speech the First Sea Lord said: ‘Make the Royal Navy “un-credible,” and we cease to be a first division player.

‘Our responsibility to the navy we command and lead, our responsibility to defence, and our responsibility to the nation we serve, is to fight to deliver a credible navy.’

The speech comes after the head of the military, General Sir Nicholas Houghton, raised concerns of cost-saving cuts on the navy after the last defence review.

As reported, two new aircraft carriers HMS Prince of Wales and HMS Queen Elizabeth are under construction. The fate of the former will be decided in the defence review next year.

And the warning comes less than a month after former US Defence Secretary Robert Gates warned Britain was at risk of no longer being a full military partner of the United States due to lost capability.

The 2010 Strategic Defence and Security Review froze the navy’s ability to operate aircraft carriers armed with fighter jets for a decade.

The carriers could be used on rotation, with one in operation and one used for training – or one could be scrapped.

And the government has yet to buy any of the F-35 fighter jets due to be on the carriers

The Times report said that Admiral Zambellas spoke last Thursday at Trinity House, London, to sailors and two defence ministers, and said anything less than keeping both carriers was not cerdible.

He added: ‘Our strategic direction will be re-defined as our nation emerges from recession, blinking into the sunlight of global opportunity.’

‘We must argue relentlessly that if we want to be a credible nation, then we need a credible navy.’