As American forces encounter stiffer resistance on the road to Baghdad, military commanders say they have been authorised to use still greater firepower.

The revelation that Daisy Cutters were used to wipe out an Iraqi Republican Guard division outside Baghdad follows the downing of two American aircraft -- a Black Hawk and an F/A-18C Hornet -- near Karbala.

According to the Pentagon, seven soldiers were killed and four wounded when small arms fire brought down the Black Hawk. The fate of the pilot of the F/A-18C was not known and US forces say they have launched a search and rescue mission.

The UH-60 Black Hawk is one of the American army's main utility and troop-transport helicopters. Each has a four-member crew and can carry up to 11 soldiers.

On March 24, an Apache helicopter went down during an assault on the Republican Guard and the pilots were captured.

The use of two Daisy Cutters is an indication that the US has stepped up attacks on the Iraqis.

The massive bombs helped destroy the Baghdad division of the Republican Guards, opening a route from the Tigris River crossing at Al-Kut, 150km from the capital.

Daisy Cutters, used in Vietnam and Afghanistan, are crude compared to cruise missiles and precision-guided bombs.

But they are considered highly effective. The size of a small family car, they have to be dropped from a specially adapted C-130 Hercules transport plane.

They contain 6,804kg of fuel-air explosives, a variation of the deadly napalm [meant to destroy targets with high temperature flame], which the US deployed with destructive effect in Vietnam.

The plane carrying the device has to fly above 6,000feet to escape being destroyed by the blast.

The bomb detonates three feet above the ground, spraying tiny droplets of fuel-based explosive into the air where they create a massive 'air burst', a huge explosion, marked by a mushroom cloud.

The blast is so powerful that it kills everything within a 600-metre radius. Anything close to the blast is incinerated, while people farther away die when the air is sucked from their lungs.

The bomb got its nickname in Vietnam, where it was used to create clearings in dense rainforest for helicopter.

In the first Gulf war it was used against Iraqi units in a bid to create panic and to clear minefields, although its effectiveness against landmines was never measured.

Daisy Cutters were also dropped on the caves of Tora Bora in Afghanistan in a bid to kill Al Qaeda and Taliban terrorists.

The US recently tested an even bigger bomb -- the 9,526kg Massive Ordnance Air Blast [nicknamed the Mother of All Bombs]. It was detonated on a test range in Florida shortly before the beginning of the war.

Rediff.com Senior Editor Shyam Bhatia is the co-author of Saddam's Bomb, on Iraq's search for nuclear weapons

External links:
http://www.guardian.co.uk/flash/0,5860,588916,00.html
http://www.washingtonpost.com/wp-srv/nation/graphics/attack/response_14.html