ABOARD THE USS CARL VINSON, in the Persian Gulf » More than a dozen Navy F/A-18 warplanes roar off this aircraft carrier every day to attack Islamic State targets in support of Iraqi troops battling to regain ground lost to the militants in June.

These Navy pilots face an array of lethal risks during their six-hour round-trip missions. Surface-to-air missiles and other enemy fire lurk below, as the downing of an Iraqi military helicopter late Friday underscored. About 60 percent of the air crews are still learning the ropes on their first combat tours.

The U.S.-led coalition improvises how the Iraqis call in airstrikes: Iraqi troops talk by radio to U.S. controllers at Iraqi command centers, who in turn talk to the Navy pilots to help pinpoint what to hit. Senior commanders have said that placing U.S. spotters with the Iraqi troops would be more effective, but they have yet to recommend that step knowing that President Barack Obama opposes it.

In the initial weeks of an air campaign that started in August, Iraq’s troops were tentative. Fighters from the Islamic State quickly learned not to move in large numbers to avoid being struck. Three out of every four missions still return with their bombs for lack of approved targets.

But in recent days, the Iraqis have been advancing, forcing Islamic State to fight more in the open. The airstrikes are severing the militants’ supply lines, killing some top leaders and crimping their ability to pump and ship the oil that they control.

"It wasn’t going so well there for a while, but the momentum seems to have reversed," said Cmdr. Eric Doyle, a 41-year-old F/A-18 Hornet pilot from Houston who also flew combat missions in the Iraq and Afghanistan wars.

About one quarter of the 1,200 total airstrikes in Iraq and Syria so far have been flown off a carrier — the other missions began from bases around the gulf — an enduring symbol of American power in the Middle East.

After Islamic State fighters rolled south into Mosul six months ago and threatened Baghdad, the Pentagon rushed the carrier George H.W. Bush to the Persian Gulf from the coast of the Pakistan, where it was flying missions in support of U.S. troops in Afghanistan.

Within two days, the carrier was sending surveillance and reconnaissance flights over Iraq and Syria. It was weeks before the United States ironed out arrangements with regional allies to allow land-based planes to carry out strikes. The Vinson relieved the Bush in mid-October and will stay until next spring.

"You don’t have to ask anybody for permission to use a carrier," said Vice Adm. John W. Miller, commander of the Navy’s 5th Fleet in Bahrain. "It’s five acres of sovereign U.S. territory."

This ship has an unusual place in the annals of the campaign against terrorism. Some of the first airstrikes of the Afghan War in October 2001 were by jets from the Vinson; nearly a decade later, it was here that Navy SEALs brought Osama bin Laden’s body after the raid in Pakistan and buried it at sea after religious rites on the lower hangar deck.

The flight deck is the bustling hub of this nuclear-powered behemoth, which is home to 5,200 sailors and officers for nearly 10 months at a time. Sailors in light helmets and tinted goggles, mostly in their early 20s, scurry about in vests and long-sleeve shirts color-coded to their jobs — red shirts handle bombs, purple shirts handle fuel, yellow shirts handle the flights.

Racks of bombs and missiles rise from elevators below deck amid the din. MH-60 Seahawk search-and-rescue helicopters buzz overhead on their way out to sea.

It is like a crowded suburban parking lot, except these are $57 million jets taxiing for takeoff with 500-pound laser-guided bombs tucked under their wings. The slightest misstep around these high-performance jets and turboprop planes could be fatal. "Beware of Jet Blast, Propellers and Rotors" is emblazoned in large yellow letters on the ship’s superstructure, lest anyone forget.

It is a dangerous business, even when the ship is not at war. In September, while training in the western Pacific, two F/A-18s from the Vinson collided in midair soon after takeoff. One pilot was rescued in the accident, but the other was killed. His body was never found in waters nearly three miles deep.

About 20 percent of the 100 daily flights are strike missions into Iraq and Syria. The others are a mix of training, supply, reconnaissance and other flights, usually between 10:30 a.m. and 11 p.m.

About an hour before takeoff, fighter pilots in flight suits stride to their planes for a final inspection. Tiny black bombs are stenciled below the cockpit for each weapon dropped from that aircraft. A giant steam-powered catapult then hurls the jets off the ship, from a dead start to more than 125 miles an hour in less than three seconds.

By then, the pilots have studied their routes, the weather and the targets assigned by an American air command center in Qatar, a tiny gulf state. Targeting specialists have selected bombs big enough to do the job but mindful of the risk to civilians.

The allied jets are operating under some of the strictest rules intended to prevent civilian casualties in modern warfare.

"If there’s any doubt, we do not drop ordnance," said Capt. Matt Leahey, a 44-year-old Naval Academy graduate from Lewiston, Maine, who commands the 2,100 personnel and 63 aircraft in the carrier’s air wing.

The Vinson has steamed to the northern part of the gulf to shorten flight times as much as possible, but it is still 450 miles to Baghdad and much farther to Syria. The F/A-18s burn 5,700 gallons of fuel on a typical mission, and pilots must refuel in midair three or four times.

The jets fly well above 20,000 feet, out of the range of most antiaircraft guns. Islamic State has surface-to-air missiles and has downed a few Iraqi helicopters, so pilots cannot fly as low as they would like to get the best look at their targets.

"Manpads are a real threat," said Doyle, referring to Man-Portable Air Defense Systems.

In some cases, pilots are striking specific, planned targets such as headquarters buildings. But most of the Vinson’s missions are targets of opportunity while safeguarding Iraqi troops below.

Pilots fly over designated grid areas, typically 60 square miles, searching for fighters, artillery and other signs of the enemy. An aerial armada of surveillance planes with names like Joint Stars and Rivet Joint track militant movements on the ground and intercept their electronic communications, feeding a steady stream of information to pilots.

"It can be pretty boring, then all of sudden it gets heated and you’ve got a whole lot of work to do in 120 seconds," said Doyle, who has flown eight strike missions so far. "We’re trying to find things and kill them."

Working with the U.S. air controllers in the Iraqi command centers — special operations troops in contact with Iraqi or Kurdish ground troops — pilots say they are aiming to weaken Islamic State’s war machine in a fight they caution could take months or even years.

"We’re taking away the enemy’s ability to reinforce and resupply," said Lt. Adam Bryan, 31, an F/A-18 Super Hornet pilot from northwestern Connecticut. "It’s a pretty dynamic situation."

Eric Schmitt, New York Times

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