In Washington, Major General Stanley McChrystal announced that two of the Guards divisions, Medina and Baghdad, were "no longer credible forces," but the Baghdad division's commander said his force was intact and ready to "confront the enemy."

The Baghdad division is a mechanized force composed of three brigades, and is stationed some 150 kilometers (90 miles) southeast of Baghdad around Kut. According to US military officials, it was "destroyed" in heavy fighting Wednesday by the First Marine Expeditionary Force.

Unlike other Guard divisions, it did not take part in the 1990 invasion of Kuwait, spearheaded uniquely by four other divisions, or face US-led forces in the Gulf War that followed.

Since 1997, the division has been stationed around the northern city of Mosul, but was recently ordered south as part of measures to beef up defenses around the capital.

The Medina and Nebuchadnezzar divisions that also confronted US-led coalition troops Wednesday south of Baghdad are renowned fighting units, Medina commanding a tank battalion of Russian T-72s while Nebuchadnezzar is reputed for its artillery.

The Medina division has already come up against the American military when, in 1991, it stood its ground and fought instead of turning tail and running as many other Iraqi forces did -- and at a cost of considerable losses.

It is deployed some 80 kilometers (50 miles) south of Baghdad, with a second line on the immediate outskirts of the capital. To the east, the Nida division is stationed and to the west, the Hammurabi division.

It was on February 27, 1991, that the US First Armored Division took less than an hour to destroy Medina's impressive array of artillery, including 61 tanks and 34 armored cars just north of the Iraq-Kuwait border.

The Adnan division, that came under coalition airstrikes Wednesday, was pushing south to defend Baghdad from Saddam's hometown of Tikrit 200 kilometers (125 miles) north, US Central Command in Qatar said.

Also equipped with tanks, the Adnan division fought against US troops in 1991 and counts a number of officer's from Saddam's tribe.

The Guard has a total fighting force of just 60,000 men and is made up of eight divisions, three of them armored, and composed of volunteers drawn from the serving army -- but only Sunni Muslims need apply; Kurds and Shiites are generally not considered up to the task and are excluded.

The heavy losses it suffered in the 1991 Gulf War have meant it has never entirely been able to rebuild its strength or its artillery, let alone modernize, amid 12 years of international sanctions.

According to the influential British publication, Jane's Defence Weekly, its divisions can only call on 500 artillery units, some 800 tanks and 1,100 armored vehicles.

Having once deployed the force around the country, Saddam handed the Guard responsibility of defending the capital.

A special unit of 15,000 men has been charged with guarding his various palaces and the only regular military presence in the capital itself.

The Guard was initially set up by Saddam as a presidential force and grew in strength throughout the war with Iran from 1980 to 1988, with its ranks swelling at one point to 150,000 men.

SPACE.WIRE