By Jonathan Marcus BBC defence correspondent

The latest attack by US and British warplanes against a command and control centre in southern Iraq has inevitably raised speculation that it may be a preliminary to a much broader air campaign.

The location of the target - well to the west of Baghdad - is unusual, though the Pentagon has moved swiftly to deny press speculation that the operation involved up to 100 warplanes.

Iraq's integrated air defence system was largely destroyed during the Gulf War - since then it has to some extent been re-built.

Only a small number of aircraft actually released weapons: The overall "strike package" including electronic warfare planes, accompanying fighters and so on, probably numbered no more than 30 aircraft.

But the key question is how this attack - described by sources in both the Pentagon and the Ministry of Defence in London as "routine" - relates to the Bush Administration's wider military plans for Iraq?

Each and every operation from now on is going to be scrutinised by outsiders to see just how it might fit into any war plan.

In reality all of the attacks against Iraqi radars, missile sites and so on, serve to gradually wear away Iraq's defences.

Outside assistance

The country's integrated air defence system was largely destroyed during the 1991 Gulf War. Since then it has to some extent been rebuilt.

While still largely relying upon old Soviet-era surface-to-air missiles the Iraqis are said by intelligence analysts to have sought to re-create some sort of cohesive national defence system.

Iraq's air defences are less than formidable

Some new equipment has been brought in from abroad.

China has been accused of assisting the Iraqis to lay a network of fibre-optic cables in the ground, to provide secure communications between command centres and missile batteries.

The Iraqis have also mounted some static weapons onto trucks to give them a greater degree of mobility.

Iraq's air defences, though, are no match for America's air power.

US and British patrols enable significant quantities of intelligence to be gathered.

The aim of any eventual air campaign will be to destroy the coherence of Iraq's air defence system as a whole and then to attack it piece by piece.

Clearly any individual operations that destroy vital elements of this network like command centres or relay stations makes the eventual task that much easier.

War footing

But the real signs of US military preparation are elsewhere.

Certain key reservists have had their call-up terms lengthened.

Iraqi tanks which survived the Gulf War lack spare parts

Military equipment is quietly on the move.

At least one additional ship has been chartered to carry armoured vehicles to the Gulf region.

Reports suggest that a heavy armoured brigade's worth of equipment - 100 M1A1 tanks, 30 Bradley armoured fighting vehicles as well as some 300 other guns, rocket launchers and transport vehicles - has been moved from Qatar to Kuwait.

This joins an existing brigade-set of equipment already pre-positioned in Kuwait.

This gives the Americans a full division's worth of equipment in Kuwait which could be activated at short notice, its soldiers flown in from the US or Germany and then deployed into the field.

This is not yet the full build-up for war. It could still be classed as prudent planning by the US military.

But the pieces are slowly being moved into position.

Some people believe that if there is a war against Iraq, it may involve a relatively small force initially - there will not be the long build-up of Operation Desert Storm hosted by Saudi Arabia, which shows every sign of wanting to see out this crisis on the sidelines.