The gigantic stone structure, which looms over Inigo Jones' ornate Banqueting House, has been completely refurbished at a cost of £352m by a PFI consortium that includes Skanska as main contractor and HOK as architect.
Like other Whitehall ministries that have undergone refurbishment in recent years, such as the Treasury, the MoD building is a classical stone building and is grade I listed.
The difference is that the MoD building is only 55 years old and is as architecturally undistinguished as it is huge – the architectural historian Sir Nikolaus Pevsner dismissed it as "a monument of tiredness".
Even so, its listed status has ensured that there is no external sign of the transformation other than stone cleaning.
Inside the 10-storey building, it is a different story. As Geoff Hoon, the secretary of state for defence, said at last week's press reception: "How much brighter and more open the building now is compared with the long, dark corridors that were there before. It was not entirely clear where my office was, which embarrassed me in the lift on the way up."
Some 5 km of central corridors passing between rows of cellular offices have been ripped out to make way for open-plan offices. Three hundred cellular offices have been slashed to just nine, though these are supplemented by 200 meeting rooms. Although there have been no extensions, the building now accommodates 3200 staff, about 600 more than before.
The physical transformation has been accompanied by the introduction of efficient working methods, such as sophisticated IT systems and the dissolution of entrenched hierarchies.
Jonathan Hoyle, the MoD's project director, said: "We have replaced the old secretive 'knowledge-is-power' approach". Now three-star lieutenant-generals will sit alongside others in an open-plan office.
One of the biggest technical problems that faced the project team was the glazing. The original aluminium windows were retained, but the gloomy blast-proof curtains behind them were replaced with secondary windows in blast-resistant reinforced clear glass.
The internal courtyards have been roofed over to turn them into attractive and comfortable staff amenity spaces. Stretching a lightweight translucent membrane, such as ETFE, across the courtyards was rejected in favour of more bomb-resistant glazing. This was so heavy that it required colonnades of steel columns and piled foundations to support it.
The total cost of the PFI, including facilities management over 30 years, amounts to £746m. However, the National Audit Office reported in April 2002 that the MoD was "likely to secure significant benefits" from the contract, such as increasing the building's capacity.
The PFI consortium comprises developers Innisfree and Equion, with Amey as facilities manager. The WSP Group was structural and services engineer and TPS the security consultant.