Britain's armed forces are over-stretched and under-funded, a group of former senior military leaders and politicians has warned.
British forces are stationed in Helmand province in Afghanistan
They have formed the UK National Defence Association, led by three ex-chiefs of the defence staff.
Gen Lord Guthrie said: "We are... struggling. I don't know how much longer the forces can go on like this."
The group says defence spending should be about 3% of gross domestic product - about 1% higher than next year.
The defence budget has been set at £34bn for next year.
In addition to Lord Guthrie, its patrons are former defence chiefs Admiral Lord Boyce and Marshal of the RAF Lord Craig, as well as ex-foreign secretary Lord Owen.
Other prominent supporters include Sir Richard Dearlove, former head of MI6, and Patrick Mercer, the Conservative MP who serves as a defence adviser to the prime minister.
Lord Guthrie, who served as chief of the defence staff under both Labour and Conservative governments, told BBC Radio 4's Today programme military spending was not enough to meet the needs of service personnel in Iraq and Afghanistan.
He added: "If they are struggling, we are in danger of damaging one of the priceless assets of our country.
"Resupplying an army in the field like in Afghanistan is not like stocking shelves at Tesco. This is an extremely complicated and dangerous thing to do."
Lord Boyce - who was chief of defence staff during the 2003 Iraq invasion - said military personnel needed to be retained once they had joined the armed forces.
"We're finding at the moment that the forces are at full stretch and we can expect to be in Afghanistan for many years ahead.
"We need to recruit soldiers, sailors and airmen and we need to retain them when they come in.
"If people are seeing that the government is not prepared to support them properly then we're not going to get those recruits, we're not going to be able to retain people and we're not going to be able to deliver the commitment we should be giving to Afghanistan and indeed Iraq."
UKNDA president Winston Churchill - grandson of the UK's prime minister during World War II - said: "At the time of the Falklands 25 years ago we were spending 5% of our gross domestic product on defence.
"Today it's down to 2.1% and we're fighting the two most intense wars we've fought since Korea."
Col Bob Stewart, a former British commander with UN forces in Bosnia, told the BBC's Breakfast that underfunding meant Britain was "sleepwalking into disaster".
He urged the public to "wake up and listen because the soldiers are suffering on our behalf".
The Ministry of Defence said it welcomed any initiative aimed at promoting informed debate about the forces.
But it added that military spending was due to rise by £7.7bn by 2011, extending the forces' longest period of sustained growth since the 1980s.
Defence Minister Bob Ainsworth launched a command paper outlining the government's strategy for improving the level of support offered to service personnel, their families and veterans.
The current chief of the defence staff, ACM Sir Jock Stirrup, said this was a "timely move" and he looked forward to being closely involved.
Mr Ainsworth told BBC News: "I don't accept that we are not properly equipped in theatre.
"We shouldn't just pluck out a figure and say this is going to be the level of spending."
The launch of UKNDA came in the wake of defence procurement minister Lord Drayson's announcement that he would take a "leave of absence" from his duties to participate in the 24-hour Le Mans motor race.
Lord Guthrie said he believed that funding shortages were behind Lord Drayson's decision.
He added: "I would think that probably - and I'm putting words into his mouth - that he was frustrated by the bureaucracy and that some of his plans for modernising procurement are just not achievable unless more money is available."