Shrouded in secrecy, San Nicolas Island is a remote spit of land in a vast, shimmering sea.

Some of the world's most sophisticated weapons are tested here, sometimes just a few hundred yards from where elephant seals trumpet in lagoons and island foxes trot through chaparral.

Tomahawk, Harpoon, Sidewinder and Sparrow missiles routinely whiz overhead. Some skim in over the waves at 500 mph to clobber fake Scud launchers or dummy radar sites on shore. Because explosives are not used, workers dig the missiles out of sand dunes and use them again.

Much of what happens on the island, about 75 miles southwest of Santa Monica, is top secret. But Navy officials recently took visitors on a carefully guided tour, in which they stressed their commitment to preserving the environment while saying that missile testing is at an all-time high.

"The workload on the air and sea range has never been higher," said Stephen Mendonca, director for test and evaluation for the island. "Our primary reason for being here is not the environment, but we do our best to protect it."

Officials say the war in Afghanistan, national security concerns and a possible confrontation with Iraq have fueled the increase in activity.

The island, owned by the government since 1933, is a laboratory for the latest generation of weapons. Some, like the Standoff Land Attack Missile, or SLAM, were seen on television during the Persian Gulf War, flying down chimneys or through windows.

Newer SLAMs can be fired from San Nicolas to the naval testing site at China Lake, in the Mojave Desert 200 miles northeast, where they navigate around buildings until they locate a designated target. A chase plane follows each missile and can destroy it if it veers off course.

"The complexity of war has changed, and you need a massive arena to evaluate systems," Mendonca said. "There are very few weapon systems that don't come through here."

The testing area around San Nicolas is 36,000 square miles, enough air and ocean to accommodate the most powerful weapons. British, Norwegian, Japanese and Italian armed forces often conduct secret tests in and around the island, as well.

San Nicolas, one of eight land masses known as the Channel Islands chain, is 10 miles long and three miles wide and has a 10,000-foot runway that can handle the largest aircraft. Sophisticated telemetry centers, shaped like enormous golf balls, dot the island, monitoring everything that flies overhead.

A small but heavily armed security force patrols San Nicolas, turning back curious boaters who try to land.

Sailors liken the place to an aircraft carrier because of its shape and isolation and the fact that it moves north at a quarter of an inch per year. The island's weekday population of about 150 military personnel and civilians drops to 30 on weekends.

"It's really a ship at sea," said Navy Cmdr. Raymond Schenk, military chief on the island.

Home for most is Nicktown, a small cluster of low-slung buildings, including dormitories and a mess hall, a small store, a bowling alley and a saloon. The island is often cold and windy, with great fog banks drifting over the land.

"It takes a special individual to live here," said Jeff Chilton, the island coordinator who has worked on San Nicolas for six years.

Chilton, who usually goes home on weekends, lives in a two-room apartment on the island. After work, he makes dinner on a small stove. He says he goes to bed by 10 p.m. or "I turn into a pumpkin." At one point, island duty took such a toll on marriages that it was dubbed "Alimony Rock," he said.

"My wife and children live in Oxnard [Calif.]. Fortunately, my wife is a very independent woman," he said. "The island has been good to me, but people either love it or hate it. There is no gray area."

According to the military, most sailors love it. Schenk said 80 percent of the personnel ask for extensions of their duty on the island.

"A lot of the island fever is kept at a minimum, because they can go home every weekend," he said. "I hear everything; I know what everyone is doing. We have very few disciplinary problems."

Talking to the military personnel was not an option. Officials steered reporters away from sailors, saying they were tired after taking part in exercises off the west side of the island.

Chris Willard, 30, a civilian bus driver from Ventura, Calif., said the place takes getting used to.

"When I first started, I felt kind of enclosed here, because you really couldn't go home at the end of the day," he said. "I have one friend here. When I am done at work, I go home and work out. I don't really do much else."

Getting to San Nicolas usually involves a 45-minute ride from Point Mugu, Calif., 65 miles away, aboard a small twin-engine aircraft. The plane flies about 6,000 feet above the ocean, making for a bumpy ride in bad weather. Heavy equipment is brought in by barges that take about 10 hours to make the crossing.

The combination of mercurial weather and rugged terrain gives San Nicolas a stark, brooding character. Sand dunes and ground-hugging succulents cover the terrain. There are few trees to break the near-constant roar of the wind.

Grunts of elephant seals fill the air as they battle for supremacy in lagoons and along empty beaches.

The rough surf seems to boil. Along one wild beach, waves from opposite sides of the island collide, creating spectacular rolling towers of water.

"We call this place Rock Crusher, for obvious reasons," said Chilton, pulling his hat down low to fend off the driving rain.

Before a missile is fired at or over San Nicolas, it undergoes rigorous tests in the laboratory.

"They do thousands of tests on computers and then maybe two or three live firings on the island," Schenk said.

But amid all this shooting and carefully planned destruction, wildlife has flourished.

Every winter, more than 25,000 California sea lions and 15,000 elephant seals breed on San Nicolas, biologists say. Island foxes, endangered elsewhere on the Channel Islands, thrive there in isolation, far from predatory birds such as the golden eagles that devour them on Santa Cruz Island.

Grace Smith, a biologist on San Nicolas, said there are 450 island foxes on San Nicolas.

"We have the highest density of island foxes anywhere," she said. "There are no threats here. I think the Navy presence has actually helped." Officials say they often juggle testing plans to protect wildlife, waiting until elephant seals or whales move to avoid accidents.

"We don't want a missile test over a pod of whales," said Paul Knight, deputy director for programs on the island.

Vegetation has been cut back a few yards on each side of the roads to keep island foxes, which like to stay among plants, from wandering into traffic. Signs warn drivers to beware.

"It surprised me, but the environmental regulations out here don't impede us in any way," Schenk said. "That a testing facility and natural resources can coexist is amazing. It's been a great education."

San Nicolas coordinator Jeff Chilton, 50, walks past a missile launcher. "The island has been good to me, but people either love it or hate it," he said.A mock Scud missile launcher is used for target practice on San Nicolas Island. A telemetry-receiving antenna dwarfs visitors to San Nicolas Island, a lab for the latest generation of U.S. weapons.