A new weapon in the Bay Area's fight to preserve its military history was unveiled Sunday afternoon. It's called Battery Townsley - a refurbished World War II underground fort in the Marin Headlands.

About 200 volunteers, history buffs, hikers passing by and relatives of those who were stationed atop this wind-swept hill overlooking Fort Cronkhite soldiered through the chilly weather for a ribbon-cutting ceremony and re-opening of the once top secret military big-gun emplacement.

Battery Townsley was built between 1938 and 1940 while war raged on the other side of the Pacific and the U.S. government decided it needed to better protect its coast. In its glory days, Townsley had two 16-inch guns that could fire a one-ton shell at a battleship 25 miles away.

Battery Townsley was kept such a secret that the descendants of the man who it was named after didn't even know about it.

"I haven't the foggiest idea how his name was chosen," said retired Col. Edwin Townsley with a laugh. His grandfather, World War I Maj. Gen. Clarence P. Townsley, is the fort's namesake.

The colonel came from Maryland to attend the dedication along with several other Townsleys. "We only found out about this place after a friend of my son sent us a picture of it about 14 years ago," he said.

That picture would have been of a dilapidated Battery Townsley, which had been battered with graffiti, broken beer bottles, mouse droppings and years of neglect. It was closed to the public in the early '90s.

Thanks to a bequest made by the late Chuck Wofford, a former National Park Service volunteer who fell in love with Battery Townsley's mysterious maze of concrete and steel, the gun emplacement is now cleaned up and open to the public. The mostly volunteer effort took 21/2 years and about $150,000 to complete with oversight from the Golden Gate National Parks Conservancy, according to John Martini, a retired park ranger and a leading volunteer of the restoration.

"World War II changed everything," Park Service historian Stephen Haller said during the ceremony. "In an age of global threat, this is an early still frame in an unruly movie that we're all still a part of. This was seacoast defense at its most advanced."

Janet Santiestevan was 10 years old living in San Francisco's Presidio when Pearl Harbor was bombed. That day she remembers her father, an army commander, hurrying off to a secret place in the Marin hills.

"My father, John Schonher, disappeared for three weeks, and I later found out he was camped inside here with his men the whole time," said an emotional Santiestevan, who, along with a group of 30 relatives, attended the ceremony and toured the grounds.

The crowd spent the afternoon meandering through the battery like a museum, which includes clues to its changing uses. The gunners at Battery Townsley actively tested the artillery during World War II. By the 1950s, the guns were scrapped and the space was used for living quarters for soldiers.

During the Cold War, it was used as an underground testing facility. And by the 1980s, it was where junior high school kids would use spray paint and firecrackers to take out their aggression.

During the 1950s, a soldier named Howard Thies would walk by the closed battery on his way down to Fort Cronkhite. One day, he saw a metal hoist out front. Figuring it was destined for scrap, he stole it.

"Actually, I guess you could say I borrowed it," said Thies, who drove from Texas to Battery Townsley to return the artifact to the Park Service.