The man snorkeling in July off Kualoa Regional Park apparently didn't see the bright orange Coast Guard helicopter circling overhead, or the 9-foot tiger shark cruising 100 yards away.

The chopper crew was keeping an eye on both.

"You see a situation like that develop, and you've got to think, what is the best thing to do?" said Lt. Cmdr. Tyson Weinert, 34, who was piloting the Coast Guard's familiar orange-and-white-striped HH-65 Dolphin that day.

The crew couldn't get the man's attention, and Weinert said he was ready to lower a rescue basket and put a swimmer in the water if the shark got any closer.

"Just the fact that we were orbiting over the shark might have caused it go in another direction," said Weinert, who's from San Diego. "It's just one of those things. You never know what you'll see on a patrol."

That patrol is one that the Coast Guard conducts almost daily. It has done so since shortly after the Sept. 11, 2001, terrorist attacks.

The "ports, waterways and coastal security" mission has become a staple of the Coast Guard nationwide. On O'ahu, the low-flying, shore-hugging Dolphins are a familiar sight and sound to kama'aina and tourists alike — even if they may not really be sure what the Coast Guard is doing.

"I was thinking what it was, because it doesn't have the writing of the police, or the color of the police," said Anna Landau, a visitor from Italy who was at Waikiki Beach recently and had seen the orange helicopters fly by.

Marilyn Dutra, 56, from California, who spends several months a year here, said the distinctive high-pitched whine of the Dolphin is enough for her to know what's coming.

"We'll be walking and hear it, and you'll know it's them," said Dutra, who has friends who run the Prime Time Sports concession in Waikiki. "I'm assuming that (coastal protection) is what they are doing."

A Coast Guard crew of three recently demonstrated what they do, flying slowly around O'ahu at around 80 knots and as low as about 200 feet on a nearly two-hour circuit.

With 1,500 pounds of fuel, the twin-engined Dolphin can fly for about 2 1/2 hours. Normally, two pilots, a rescue swimmer and flight mechanic are on board. To a lesser extent, the Coast Guard also flies Neighbor Island coast security patrols.

The missions are one outgrowth of 9/11 and homeland security concerns. Another was the addition in 2004 of armed Coast Guard Maritime Safety and Security Teams operating from small boats and intended to be a fast-response measure.

For fiscal 2007, the Coast Guard flew 360 flight hours on the coast security missions in Hawai'i — a fraction of the 5,780 hours flown by the helicopters on all missions, which typically include about 350 search-and-rescue flights a year.

But the coastline flights remain the most visible and familiar aspect of the service's duties.

Although the crews flying the coast missions are on the lookout for suspect ships or harbor activity, that's not all they do, and the flights most often end up being about assisting with waterway safety and environmental compliance.

"The Coast Guard prides itself on being a multi-mission asset," Weinert said over the crew communications link.

Flying west from Barbers Point, where the Coast Guard's Dolphins and C-130 fixed-wing aircraft are based, Weinert made a circle around Barbers Point harbor and a foreign tanker, and also passed by the offshore fuel loading points.

The Kahe Point power plant is on the flight checklist, and the tourist boats that gather in the area also get a look.

Lt. John Titchen, a Coast Guard spokesman, said "the idea, essentially, is to be a deterrent (to illegal activity) as often as we can."

The Coast Guard enforces the Marine Mammal Protection Act, and close to a year ago, some tour boat operators were spotted working together to try to herd dolphins just outside Pokai Bay, in violation of environmental rules, Weinert said.

"Most boats behave themselves," said the pilot, who has been flying Dolphins in Hawai'i and elsewhere for six years.

About eight months ago, a couple of kayakers had been swept out to sea by currents off Ka'ena Point, Weinert said. They had food, water and a radio, and were not in danger of being swamped, but were too far out to make it back, he said.

"Safety is paramount to us," Weinert said. "If I don't have to go to a hover and put (a rescue swimmer) ... in the water, I won't. So we flew around and I talked (by radio) to one of the boaters and asked if he'd be a good samaritan and pick them up."

Before the flight, Weinert went through a battery of preflight checks, including 48 items before the engines were even started. The Coast Guard had four Dolphins in Honolulu, but one crashed at sea Sept. 4, killing all four crew members aboard. Before that, the most recent crash and loss of life for a Barbers Point aircrew had been in 1982.

During the coast security flight, the three crew members had their heads swiveling, examining not only the shoreline below but the sky above and the ground in between.

The crew had to keep their distance from a private jet taking off from Barbers Point, a Stearman biplane flying overhead and two powered kite planes in Hale'iwa, a private Robinson helicopter that didn't reply when contacted, Navy P-3 Orion sub hunters near the Marine Corps base in Kane'ohe, an Army Chinook helicopter in the vicinity of Hanauma Bay, and F-15 fighters from the Hawai'i Air National Guard.

The Coast Guard tries to fly low enough to see what's happening below, but high enough or far enough away to avoid disturbing people, Weinert said.

Flying restrictions vary by location, and over the Nu'upia Ponds next to the Marine base, Weinert flew at 800 feet. In the vicinity of Honolulu International Airport, the Coast Guard has to fly below 300 feet.

The Dolphin circled around both Honolulu Harbor and Ford Island, providing a lingering look at the ships and facilities below.

"The Navy has a really good harbor security force," Weinert said. "It's just nice to work with them."

Petty Officer 1st Class Joshua Ewing, 36, who was on the flight, said he normally carries a still and video camera on the missions to document activities of concern.

The Santa Cruz, Calif., man is an aviation maintenance technician, but also gets in plenty of flight time.

"One minute I can be working on the aircraft, and the next minute I can be flying on the aircraft," he said.

A normal week with the Dolphin crews can include training to deliver the rescue basket at sea, rescue swimmer practice, pilot proficiency training, the coast security missions, and emergency calls.

Petty Officer 3rd Class Mike De Nyse, also a spokesman for the service, said the Coast Guard can't discuss any homeland security threats that may have been investigated.

Coming up, the Dolphin crews will perform whale sanctuary flights to ensure ships are not interfering with the animals.

Both Ewing and Weinert said they were deeply affected by the loss of the four crew members in the Sept. 4 crash.

"I worked with all of them," Ewing said. "Initially, when I got back on the helicopter, my thoughts were, hey, that could have been me. But as a whole, the Coast Guard really came together to back us up."

A collage of photos of the lost crew members, some smiling with family members and friends, is posted on a wall in the hangar.

Both Ewing and Weinert appreciate being able to do the job they do, and Weinert said he tries to make sure junior crew members don't take that job for granted.

With America's current heightened posture in homeland security, "it's an interesting time to be part of the mission here," Weinert said.