Britain's military commitments in Iraq and Afghanistan brought the Army close to the point of "seizing up", a former head of the service has said.
General Sir Richard Dannatt said the decision to deploy a task force to Helmand in 2006 at a time it was facing worsening insurgency in Iraq represented a "perfect storm" for the Army.
Giving evidence to the official Iraq Inquiry, he disclosed that he had written to the then defence secretary Des Browne to warn him that morale was "fragile" and could lead to a potentially devastating exodus of personnel from the service.
Gen Dannatt said he had been surprised by the decision in 2004 to send British troops to Helmand, even though he was at that time the commander of the Allied Rapid Reaction Corps which was due to be deployed. When he took over as the Chief of the General Staff in 2006 - the year the Helmand taskforce was deployed - he was in charge of an Army that was "running hot".
"You can run hot when you are in balance and there is enough oil sloshing around the engine to keep it going. When the oil is thin, or not in sufficient quantity, the engine runs the risk of seizing up," he told the inquiry. "I think we were getting quite close to a seizing-up moment in 2006."
Commanders had been worried they would not be able to withdraw troops as quickly had been hoped from Iraq following the invasion in 2003, while at the same time having to find additional forces to deploy to Afghanistan. "We could see that perfect storm coming to fruition in about the middle of 2006 and I would contend that it did," Gen Dannatt said.
His predecessor as head of the Army, General Sir Mike Jackson, told the inquiry that by that time there was so much momentum behind the Helmand deployment it was difficult to draw back.
"I think the view was we could not suddenly put up our hand and say, 'We can't do this in Afghanistan'," he said. "Because it was not just a matter for us. It would have been the whole Nato effort in that country which would have been quite severely disrupted."
The inquiry also released newly declassified documents which showed that Gen Jackson warned five years ago that British forces in Iraq were suffering from a lack of helicopters. "Our support helicopter fleet is creaking badly...The overall picture is one of an SH (support helicopter) force ill-matched to support current operations," he wrote.
The inquiry was adjourned to Friday.