By Caroline Wyatt
Defence correspondent, BBC News
There is debate over the type of wars that will be fought in future
The heads of the Army and the Royal Navy have been setting out their priorities for defence spending in the future, ahead of what are widely expected to be painful cuts after the general election and the defence review.
Despite some areas of agreement, for example that Britain must first define its national interest and prepare and configure its forces accordingly, all three service chiefs are having to fight their corner ahead of difficult debates on how to fund all three services in the future.
The RAF is already feeling the effects of the recent "reprioritisation" in defence spending to help pay for the campaign in Afghanistan.
The head of the Army, General Sir David Richards, has warned that the UK needs to focus on what it wants to do before it decides how much to spend and must look closely at the way that the wars of the future will be fought.
He told an audience at the International Institute for Strategic Studies in London on Monday that more specialised soldiers should be trained to win over the hearts and minds of foes, along with more unmanned drones, helicopters and transport aircraft to support those efforts, as well as more focus being put on intelligence gathering and cyber warfare.
He said less money should be spent on expensive hardware such as large warships, tanks and fighter jets, which he believes will be of more limited use.
Outlining his vision of future conflicts, General Richards predicted that even wars between nations were more likely to resemble the conflicts in Afghanistan and Iraq than traditional state-on-state warfare, with such conflicts largely being fought by proxies in the form of insurgencies and economic and cyber attacks.
In his view, that would enable other countries, as well as militant groups, to cause maximum disruption using the minimum resources.
Two aircraft carriers have been commissioned by the MoD
To counter such threats, he said the UK needed nimbler, more flexible forces of its own, with specialist expertise, including a larger number of highly-trained soldiers who understood their enemy and the people of the countries in which they were deployed.
His views in the battle over the future shape of Britain's armed forces were countered on Tuesday when the First Sea Lord, Admiral Sir Mark Stanhope, launched his defence of the Royal Navy and its role in protecting the UK and its interests.
In what many will see as a direct riposte to the idea that Britain has put too much emphasis on "hugely expensive equipment", Admiral Stanhope said that the UK's influence and commercial interests depend on a fleet that can operate worldwide with full capabilities, including high-intensity warfare.
Both the head of the Army and the Royal Navy agree that Britain must debate and prepare itself properly for future conflicts, and that prevention of wars is better than cure.
However, Admiral Stanhope argues that the armed forces must look beyond the example of Afghanistan.
Where the head of the Army argued for more specialised and highly skilled soldiers, the head of the navy cited the Falklands as the type of strategic shock that the UK must remain fully prepared to counter.
Admiral Stanhope also challenged the Army's view that expensive defence equipment, such as the two new aircraft carriers on order for a total of £5bn, are not the best use of diminishing defence resources.
He said that the Royal Navy contributes significantly to the overall business of defending Britain's interests as a maritime nation across the globe, citing its operations in the Gulf over the past 30 years as an example.
Navy chiefs fear that some projects, including the two new aircraft carriers as well as the US fighter jets to put on them, plus the replacement Trident submarine nuclear missile system, could fall victim to cuts in the defence review.
Both Admiral Stanhope and Air Chief Marshal Sir Stephen Dalton, the chief of the air staff, are believed to disagree with General Richards' view that conventional "state-on-state" wars are a thing of the past.
The Admiral said that the two carriers are essential to project British influence around the world in the coming decades.
In his analysis of Britain's future defence needs, General Richards argued that the need to adapt to tomorrow's wars represented a "horse to tank" moment in the history of warfare, comparing it to the revolution in military tactics during World War I.
While some may dismiss this week's contributions by the chiefs as inter-service rivalry, the arguments being made by all three both internally and externally matter, and will shape Britain's ability to defend itself and project both soft and hard power, and influence, long into the future.
New equipment such as fighter jets is hugely expensive
The last full defence review was held in 1998, and Britain has found itself fighting lengthy wars in ways that were not envisaged or budgeted for at the time - one of the many reasons that British forces have had to rely increasingly on "urgent operational requirements" in both Iraq and Afghanistan.
All three services are keen for the defence review to work out how Britain defines its national interest, and work from there on how that can best be secured, rather than by focusing first on what the UK can afford, as many fear it will.
A recent review of the procurement budget showed a black hole of tens of billions of pounds of unfunded equipment.
This suggests major and often unpopular cuts will have to be made by the next government, rather than the salami slicing or delaying of projects that has become the default position for defence procurement in recent years.
This has managed to balance the books in the short term while shunting the undoubted pain of difficult decisions into the future.