The highly classified bomb creates a brief pulse of microwaves powerful enough to fry computers, blind radar, silence radios, trigger crippling power outages and disable the electronic ignitions in vehicles and aircraft.
Iraqi satellite TV, which broadcasts 24 hours a day outside Iraq, went off the air around 4:30 a.m. local time (8:30 p.m. ET Tuesday). Iraq's domestic television service was not broadcasting at the time.
Officially, the Pentagon does not acknowledge the weapon's existence. Asked about it at a March 5 news conference at the Pentagon, Gen. Tommy Franks said: "I can't talk to you about that because I don't know anything about it."
The use of the secret weapon came on a day that saw intense action on the battlefield. The Pentagon said the U.S. Seventh Cavalry killed between 150 and 500 Iraqis after being attacked by rocket-propelled grenades near An Najaf in central Iraq. There are no reported American casualties.
In other major developments:
CBS News Correspondent Byron Pitts, traveling with the Marine 7th Regiment on the road to Baghdad, said Tuesday's sandstorm reduced visibility down to about five feet. By that time the commanders sent out the order for all the vehicles to stop – tanks, armored personnel carriers, Humvees, trucks – all at a standstill because of the storm.
The weather also thwarted relief efforts. Thunderstorms hit the Iraqi port of Umm Qasr, slowing efforts to get the port open to ships carrying medicine and other provisions.
Despite the adverse weather, the U.S. still fired about 90 cruise missiles Tuesday, and Navy and Air Force jets were scheduled to fly 1,400 missions.
American officials issued fresh cautions Tuesday about the possible use of chemical weapons by Iraqi troops, although no weapons of mass destruction have yet been found by advancing coalition forces.
Asked about reports that Republican Guard forces ringing Baghdad have been given authority to use chemical weapons, Secretary of State Donald H. Rumsfeld cited "scraps" of intelligence suggesting that the closer the 3rd Infantry gets to the capital, the greater the danger.
Rumsfeld also cautioned that the war had a long way to go. "We're still, needless to say, much closer to the beginning than to the end," he said.
Still, President Bush forecast victory during a visit to the Pentagon. "The Iraqi regime will be ended ... and our world will be more secure and peaceful," he said.
Details were sketchy about the situation inside the southern city of Basra, Iraq's second-largest with 1.3 million residents. British journalists reported that residents were staging an uprising against pro-Saddam forces and that Iraqi troops were firing mortars at them.
A senior British commander, Maj. Gen. Peter Wall, said "We don't know the scale" of any revolt, but added, "Of course we would be very keen to capitalize on it."
U.N. Secretary-General Kofi Annan and others have warned of a possible humanitarian crisis in the city. The International Red Cross said during the day that it had begun repairs at a war-damaged water-pumping station serving the city.
At its headquarters in Rome, the World Food Program announced Tuesday it was launching its biggest appeal ever for emergency aid to feed Iraqis for about six months.
"We expect that we will be asking for over $1 billion," spokesman Trevor Rowe said. "We anticipate that this could well turn into the largest humanitarian operation in history."
Thus far in the campaign known as Operation Iraqi Freedom, Americans said they had taken more than 3,500 Iraqi prisoners. There was no accurate death toll among Iraqi troops or civilians.
American losses ran to 20 dead and 14 captured or missing. The remains of the first two to die were flown overnight to Dover Air Force Base in Delaware.
A total of 20 British troops had also died, including two killed Monday by friendly fire.
The U.S. Central Command announced the capture of an Iraqi military hospital used as a military staging area. Officials said Marines confiscated more than 200 weapons and stockpiles of ammunition and more than 3,000 chemical suits with masks, as well as Iraqi military uniforms. The Marines also found a T-55 tank on the compound.