By Gavin Stamp
Political reporter, BBC News
Bob Ainsworth has been under pressure since taking on the role
Being defence secretary is a difficult job at the best of times.
Having to face the public when a British soldier dies on active service is tough enough.
But the frequency with which Bob Ainsworth has had to do this in the past month, as the death toll in Afghanistan has mounted, has been particularly trying.
Mr Ainsworth, who has been in the job just over a month, is also bearing the brunt of growing opposition anger over the UK's strategy in Afghanistan.
From the issue of whether the Army has enough helicopters or armoured vehicles at its disposal to whether ministers did or did not turn down the army's request for an extra 2,000 troops earlier this year, he has been taking the flak.
Mr Ainsworth's own suitability has been called into question following his surprise elevation to the job during last month's emergency cabinet reshuffle.
Critics argue he lacks the political clout to fight for the resources - both in terms of troops and equipment - needed to achieve the UK's objectives in Afghanistan.
Ex-Foreign Secretary Lord Owen says Gordon Brown should create a new Cabinet role to co-ordinate the UK's military, diplomatic and aid efforts in the region - effectively operating over the heads of current ministers.
While there seems no chance of this happening, questions over leadership at the Ministry of Defence and its effect on the Afghanistan mission are unlikely to go away.
Fairly or unfairly, the top job at the MoD has come to be seen as something of a revolving door.
When he was promoted from the position of armed forces minister in June, Mr Ainsworth became the fourth defence secretary in as many years - following in the footsteps of John Hutton, Des Browne and John Reid.
This contrasts with Geoff Hoon's almost six year spell in the role between 1999 and 2005.
Such a rapid turnover is perhaps unsurprising in such a demanding role but it has not gone unnoticed in the armed services at a time of acute pressure in Iraq and Afghanistan.
Mr Hutton, who is standing down as an MP at the next election to pursue other interests, was accused of "dereliction of duty" by Field Marshal Lord Bramall for exiting at a time when the conflict in Afghanistan was escalating.
His predecessor Des Browne was criticised for combining the role of defence secretary with that of Scottish secretary, leading to accusations he was a part-time figure.
The former Head of the Army, General Sir Michael Jackson, said he had worked with three defence secretaries in his three and a half years in the job.
"I think, as a matter of principle, it is better that such key positions as defence secretary are held on a longer term to provide that continuity," he told the BBC's World At One programme.
Figures of stature
Having several defence secretaries in quick succession has been "unhelpful", says Michael Codner, director of military sciences at the Royal United Services Institute.
Defence secretaries need "stature and respect" to make their mark, he says, and this has to be earned over time.
Denis Healey said defence was the most rewarding job in government
"There have been some very powerful defence secretaries such as George Robertson and Michael Heseltine, individuals with very strong personalities," he says.
"Getting appropriate funds for defence out of the Treasury does reflect on the clout of the individual."
Recent holders of the role have either been regarded as "safe pairs of hands" or makeweights, he says.
One reason for this was Tony Blair's hands-on role in foreign policy which saw him virtually assume the duties of defence and foreign secretaries after 9/11, with Mr Hoon largely in the background.
Gordon Brown appears to take less interest in foreign affairs than his predecessor but there are questions about the status of the defence brief after it appeared 21st out of the 23 Cabinet jobs listed on the Downing Street website.
LABOUR DEFENCE SECRETARIES
George Robertson: 1997-9
Geoff Hoon: 1999-2005
John Reid: 2005-6
Des Browne: 2006-8
John Hutton: 2008-9
Bob Ainsworth: 2009
In years gone by the role was filled by numerous political heavyweights.
Once such figure, Denis Healey, says it was the most rewarding job he did in government.
Crucially, he believes that his military service in World War Two gave him a real rapport with the job and an understanding of what it meant to send people to war.
Such experience is sorely lacking now, observers say.
"With a defence review underway, and a war on, the times need a Denis Healey," says Peter Hennessy, Professor of Modern History at Queen Mary, University of London.
"But British politics doesn't produce people like Denis anymore."
Test of judgement
While it may be unrealistic to expect defence secretaries to be battle-hardened themselves, sound judgment is clearly vital in a job where potential flashpoints are never far away.
During his time at the MoD, Michael Heseltine is probably best remembered for the manner of his acrimonious exit over the Westland affair than anything else.
Fighting a war puts a defence secretary uniquely in the spotlight
And despite winning praise for his handling of the Falklands campaign, John Nott resigned several months afterwards.
Before he did so, he stormed out of a BBC interview after being questioned about defence cuts and accusations that he was "here today, gone tomorrow" politician.
Mr Ainsworth has tried to be candid with the public, warning that more lives will be lost in Afghanistan but that the mission is necessary and ultimately winnable.
In the post-Cold War world, defence secretaries do not have nearly as much to spend as those in health and education.
However, the UK still spends more on defence than almost any other country except the US and China and budget decisions are always sensitive.
Key decisions are due in the near future over Trident renewal and the cost of two new aircraft carriers, all against a backdrop of a likely deep squeeze in spending.
While the defence secretary will play an important role in shaping the future size and scope of the armed forces, it is the PM who decides where they are committed.
Drawing a parallel with 1940, defence analyst Michael Codner says Gordon Brown is ultimately responsible for explaining the UK's purpose for being in Afghanistan and trying to carry public opinion.
"Winston Churchill made himself minister of defence as well as prime minister in reflection of the intense nature of the war," he reflects.
While not suggesting Gordon Brown follows this course of action, he says the prime minister must be upfront about what is needed in Afghanistan to succeed.
"It is obviously prime ministers who have to fight wars. They are not fought by defence secretaries. And this is a war."