Admiral Sir Mark Stanhope says the navy is vital to the UK's interests
The UK must look "beyond Afghanistan" and maintain a Royal Navy fleet able to operate with full capabilities around the world, the First Sea Lord has said.
Admiral Sir Mark Stanhope said the Afghan conflict was not the "only game in town".
He warned that the Navy had to be ready for "surprises and strategic shocks", like the Falklands invasion.
On Monday, the head of the Army called for a shift in defence spending, with less emphasis on expensive equipment.
The BBC's defence correspondent Caroline Wyatt said Army chief Gen Sir David Richards and Adm Stanhope agreed that Britain must be well-prepared for future conflicts, and that prevention was better than cure.
However, their visions for how that should be done differed in some key aspects, she added.
Both men are making their case ahead of a major review of defence spending.
Adm Stanhope said Britain must "have the strategic flexibility to deal not just with Afghanistan, but also the broad range of other threats and challenges to our national interests today and in the future".
He acknowledged the "public funding challenge," but said a threat like the Falklands War could come "in from the left field" at any time.
Caroline Wyatt, BBC defence correspondent
Many will see Admiral Stanhope's arguments as a direct riposte to the idea that Britain has put too much emphasis on "hugely expensive equipment".
He says the UK's influence and commercial interests depend on a fleet that can operate worldwide with full capabilities.
Where the head of the Army argued for more specialised and highly skilled soldiers, the head of the Navy cites the Falklands as the type of "strategic shock" that the UK must remain fully prepared to counter.
On Monday, Gen Richards told the International Institute for Strategic Studies that there was too much emphasis on cutting-edge military hardware and not enough on training troops.
"Our armed forces are primarily structured and equipped for the last war, for a war of technology against technology, armour against armour," he said.
"We have pared down our forces numbers, replacing people with hardware and thoughts with process."
But Admiral Stanhope said the "soft power" of individual soldiers depended on the "underpinning credibility" of "hard power".
As an example, he cited the controversial replacement of the Trident nuclear submarine system - something senior Navy figures worry could be scrapped to save money, but something he said was vital "to deliver the ultimate security guarantee of our nation".
The Navy was also concerned that two new aircraft carriers, costing £3.2bn, could also be mothballed or delayed, but Admiral Stanhope said these would benefit the entire armed forces.
"We have got to be clear that the requirement for the carriers is part of a joint requirement for defence as a whole, and the effect they provide is a joint effect, not a maritime effect in isolation," he said.
But Admiral Stanhope, breaking off from his set speech in London on Tuesday, denied he was in conflict with Gen Richards, insisting that "much" of what the army chief had said "resonated" with his own views.
"Whilst there is a desire to see a split between us and indeed, if I may say so, a frenzy of 'chiefs again at loggerheads' - we are not.
"What we are trying to do is pursue a clear well-articulated debate about what defence needs."