NORTH PERSIAN GULF — The black of night isn't enough to cover enemy ships from Chance Pace.

The Kamas native can spot a friend or foe from a mile away. If he doesn't, hundreds of lives are at stake. Pace, 22, mans a 50-caliber machine gun on the USS San Jacinto every night on watch for terrorists interested in taking out two oil platforms nearby.

The oil from the Al Basrah Oil Terminal and Kwahr Abd Allah Oil Terminal pump nearly $11,000 a second into Iraq's economy, and fuel 85 percent of the redeveloping country's total gross domestic product. Protecting the platforms can be tiring and mundane at times, but there is no room for error.

"If I'm off for just one second, something terrible could happen," Pace said. "I drink lots of coffee."

Even during a 2-7 a.m. shift of staring into the dark depths of the sea, Pace must be alert. He's required to make split-second decisions on what each boat's intent is, whether it be a lost fisherman or a terrorist ready to strike.

Pace looks for a variety of characteristics to spot an enemy ship: speed, direction, markings on the boat and the flags they fly.

"I have to keep my eyes open at all times," Pace said. He is one of 400 sailors aboard the USS San Jacinto, a warship that carries the most advanced underwater surveillance system available.

Enemy ships must stay at least 3,000 meters away from the oil platforms, and receive a warning if they wander within 5,000 meters. The USS San Jacinto's crew will use a variety of tactics to warn the ships away, like flares or loudspeakers telling them to move in a variety of Middle Eastern languages.

If a ship ignores those warnings, people like Pace could be directed to fire, said Lt. Cameron Havlik. From his watch at the bow of the ship, known as the forecastle, Pace can choose from twin 50-caliber machine guns, a 12-gauge shotgun and flares, although he has yet to fire a single shot from any of those guns.

Enemy ships are easier to spot in the sunlight, but Pace said he's learned to adjust in the dark. However, at times when his eyes just won't adjust, Pace carries night-vision goggles.

"Any kind of threat is going to be dark, they aren't going to be lit up like a Christmas tree. You've really got to look for them," he said.

The North Persian Gulf is so shallow that Pace doesn't have to tend to his regular duties. In deeper waters, Pace works as a sonar technician and is on the lookout for submarines and other enemies lurking beneath the water.

From the look of his sonar screen and the sound of every blip, he can determine whether a valid threat is under way.