The chair of the Public Accounts Committee Margaret Hodge has described the Ministry of Defence's management of its budget as "reckless and irresponsible".
The Ministry of Defence's top civil servants - Permanent Under Secretary Sir Bill Jeffrey and his deputy Ursula Brennan - gave evidence to the committee on 13 October 2010 following a critical report by the National Audit Office.
The report was critical of the department's budgetary management, including the management of weapons programmes and renegotiations of contracts.
Sir Bill Jeffrey admitted they had faced financial pressures but hadn't realised they were heading for an overspend.
The session comes just a few weeks before the government finalises its Strategic Defence Review.
Prime Minister David Cameron has already said he would "take no risks with British security" ahead of the review.
In a leaked letter, Defence Secretary Liam Fox has warned "draconian" cuts to defence spending would result in "grave consequences".
Dr Fox has promised fewer civil servants and senior officers, to ensure enough money is devoted to the front line.
Annual defence spending in the UK currently stands at about £37bn, which is around 2.5% of GDP. Cuts of 10-20% are expected.