French President François Hollande inaugurated France's version of the Pentagon on Thursday, a massive new defence ministry complex with walls designed to withstand a missile strike and a highly secure operational room hidden underground.

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The inauguration of the new building was "a historic step for the ministry of defence, which has finally brought all its forces (land, air and sea) together on the same site”, the French president said.

About 9,300 military and civil staff who were previously dispersed around a dozen different sites are now based in the €4.2 billion euros building, dubbed the "French Pentagon".

The joining together of army, air force and navy headquarters will make it easier to lead France's military operations abroad, said Jean-Paul Bodin, secretary general for the administration of the defence ministry.

"This enables us to be in contact with each other much more easily than before and also to mobilise the staff quicker when needed," he said.

Bodin said the new military organisation will also make the military's decision-making process "more efficient".

France's military is highly active internationally, with about 7,000 French troops involved in operations around the world, including in the coalition against the Islamic State (IS) group in Iraq and Syria as well as in operations against extremists in Africa's Sahel region.

An additional 7,000 troops have been mobilised to patrol sensitive sites across France following attacks in Paris in January on satirical newspaper Charlie Hebdo and a kosher grocery that left 20 dead, including the three Islamic extremist attackers.

It will also help reduce costs and staff in the headquarters, as part of a government plan to reduce France's military from 270,000 people to 240,000 by 2019, Bodin said.

The ministry's employees left behind historical buildings in the centre of Paris for the new modern site, in a quiet district in the south of the capital.

Yet Defence Minister Jean-Yves Le Drian keeps his office in a prestigious Paris mansion from the 18th century, closer to Parliament and the Elysée presidential palace.

The new ministry is called the "Hexagone-Balard" in French -- the hexagon being the shape used to describe France's mainland and also the shape of the heart of the building.

From the outside, the seven-storey structure looks like a modern fortress with its white opaque glass front. It is topped by the largest solar-panelled roof in Paris.

Inside it evokes a small university campus, with its succession of gardens surrounded by blue and green facades, and a series of facilities including a hairdresser, library, swimming pool, sports rooms, restaurants and preschools for the staff's children.

The specific military equipment being housed within is being kept top secret -- even from the architects.

(FRANCE 24 with AP)

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