Allied warplanes attacked Iraqi troop strongholds, bridges and missile launchers Friday, but Defense Secretary Dick Cheney said ground and amphibious assaults are still needed to make Saddam Hussein's soldiers more vulnerable.

Cheney and Gen. Colin Powell, chairman of the Joint Chiefs of Staff, arrived in the Persian Gulf Friday to assess the status of the war. Cheney told airmen and women that they are leading "the most successful air campaign in the history of the world."As the campaign continued, U.S. warplanes knocked out an Iraqi mobile missile launcher and scored possible hits on three others overnight, the military said.

Off the coast of Kuwait, a British Royal Navy helicopter blew up an Iraqi patrol boat with a Sea Skua missile, a pool report said. Iraq's naval fleet is all but out of commission, with most of its vessels either sunk or destroyed.

On land, U.S. Marine gunners fired more than 100 rounds at a suspected Iraqi artillery battery in Kuwait, a pool dispatch said. Iraqi troops did not return fire, and no U.S. casualties were reported.

It was the first ground action near the northern Saudi border since Monday, when Marines exchanged small arms, 25mm cannon and artillery fire with Iraqi troops in southern Kuwait.

In Baghdad, allied air attacks diminished overnight, but a bridge and a communications center were demolished, an Associated Press reporter said.

At separate briefings, U.S. and British military spokesmen said more Iraqi warplanes fled to Iran Friday. They said 147 Iraqi warplanes were now in Iran, up 13 from U.S. estimates Thursday of 134.

Combined with the 135 Iraqi planes that have been destroyed in the air or on the ground, about 40 percent of Iraq's air force now is out of action. Those planes in Iran include 21 of Iraq's best fighter-bombers, said the U.S. military spokesman, Marine Maj. Gen. Robert Johnston.

Johnston, responding to a question, said U.S. forces were prepared to defend themselves if the planes in Iran again took to the skies.

"From Day One we've been prepared to defend our forces 360 degrees," Johnston said, noting that Iran has repeatedly stated that those planes are grounded for the duration of the war.

The Saudi commander said Friday that allied forces have taken more than 900 Iraqi prisoners since the war began, and more than 400 Iraqi troops surrendered in the 5 1/2 months before the war. Lt. Gen. Khalid bin Sultan told reporters the POWs have told of Iraqi "execution battalions" positioned behind the front lines to kill deserters and intimidate those considering fleeing the Iraqi forces.

Cheney and Powell arrived at an air base in western Saudi Arabia and addressed several hundred people there.

Powell elicited cheers when he told them: "We'll get this over with a simple process - we're going to cut it off and kill it."

After the base visit, Cheney flew to Taif and met with the exiled emir of Kuwait, Sheik Jabir al-Ahmad al-Sabah.

En route to the gulf, Cheney publicly raised for the first time the prospect of a limited ground campaign, rather than an all-out assault.

"You add the amphibious element or the ground forces in the fashion that forces him (Saddam) to move out of his prepared positions, and it's moving out of those positions that makes him vulnerable once again to the air force," Cheney told reporters traveling with him.

Since the war's early days, Iraq has used truck-mounted launchers to fire rockets at Israel and Saudi Arabia, and allied warplanes have worked to hunt down the launchers.

U.S. military officials in Saudi Arabia reported some successes Friday. They said one mobile missile launcher in southern Iraq, aimed toward Saudi Arabia, was destroyed. Three others, in western Iraq, aimed at Israel, were damaged or destroyed, they said.

The raid in western Iraq came minutes after the Iraqis shot a modified Scud missile at the Saudi capital of Riyadh. A Patriot missile interceptor blew it apart early Friday, and no injuries were reported.

U.S. officials also disclosed that, contrary to previous assertions, Iraq still has some of its fixed Scud launch sites in addition to the mobile launchers. But they said as far as they knew, none of the fixed launchers has fired a missile since the fighting began.

In the abandoned Saudi seaside town of Khafji, which Iraqi troops briefly held last week, Saudi soldiers were still hunting down a few Iraqi stragglers, the Qatar news agency said. Citing military sources, it said the Saudis had captured 28 Iraqi holdouts and had one building under siege.

The Iraqi capital experienced far fewer bombing and missile strikes late Thursday and Friday than it did the previous night. But a major communications center was destroyed, and the al-Jomhouriya bridge over the Tigris River, left partly intact after two earlier strikes, was demolished, according to AP reporter Salah Nasrawi.

French President Francois Mitterrand predicted Thursday that the allies will mount a land offensive within a few weeks.

"The ground battle promises to take place in coming days, in any case sometime this month," he told French television reporters.

The British commander in the gulf, Lt. Gen. Peter de la Billiere, said he believes the land war is "inevitable."

If and when a land war begins, the U.S. commander in the gulf, Gen. H. Norman Schwarzkopf, says a simple frontal assault on Iraqi entrenchments would be unlikely.

"The dumbest thing you do is go right into the teeth of the enemy and play his game," he told ABC's "PrimeTime Live" on Thursday night. "We're not going to play his game out here."