Other mines were dropped in surrounding waters, but haven't been recovered. The Navy will survey the areas to recover any remaining buoyant mines.

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An inert mine that was blown up after it was found floating in the water off Bainbridge Island on Tuesday was from an exercise conducted in 2005, the Navy said Thursday.

The exercise was conducted by the Naval Undersea Warfare Command to test unmanned underwater vehicles’ ability to locate submerged objects and avoid obstacles, said Wendy Miles,  the command spokeswoman.

The Navy said 29 inert training mines were placed in areas between Brownsville, Keyport and Bainbridge Island for the exercise. Of those, four were buoyant and would float, but had been anchored to the ocean floor, Miles said. All four buoyant mines have now been accounted for, Miles said, but the Navy will conduct a survey to identify any underwater objects that could be a concern to the public. Miles could not confirm if there are other buoyant mines in the region.

An explosive device was drifting Tuesday afternoon near the Port Brownsville Marina in Kitsap County. The Coast Guard moved it to deeper waters and detonated it shortly after 8 p.m. (Mike Griffith/KIRO 7)

The mine, a sinister-looking large, round object with rods protruding from it, was spotted floating Tuesday evening about 400 yards east of Brownsville Marina in Kitsap County by officials from the state Department of Natural Resources. Brownsville is a few miles south of Naval Base Kitsap’s Keyport base.

The Navy initially said the device “appears to be a decades-old military mine of unknown origin,” leading navy historians and military technology experts to speculate it was an old training mine.

The mine was manufactured by the Naval Undersea Warfare Command to model a foreign mine, Miles said.

The Navy was unsure at first if the mine was inert and didn’t believe it could be safely towed to shore for further examination. Instead, the mine was blown up on the water Tuesday night. Boat traffic in and out of the Brownsville Marina was stopped and residents who lived along the shoreline were told to stay in place and off the beaches.

 

The mine was determined to be inert when the primary explosion did not trigger a second, larger blast. But the floating mystery mine brought up questions about what other devices might be found beneath the surface in Puget Sound.

A Navy spokesperson said Thursday evening she doesn’t know if active mines were in the Sound during or after WWII, but Seattle Times archives and local residents say the history of mines in the region stretches back to the beginning of the last century.

Electrically-controlled mines filled Rich Passage during World War I, placed there by soldiers from Fort Ward on Bainbridge Island, but were removed after the war, according to an archived Seattle Times article from 1941.

The Navy has not yet confirmed whether active mines were used in Puget Sound during WWII, but archived articles show the Navy was concerned about enemy mine warfare during this time.

A former ferry boat captain recounted the reaction in Puget Sound to the attack on Pearl Harbor in a 1963 story for The Seattle Times. “For the next few days, while the Navy was organizing a minesweeping force, the sound of rifle fire could be heard in main channels as the water was peppered with bullets calculated to explode any enemy mines,” Grahame F. Shrader wrote. Minesweeping and anti-submarine nets in the Sound during the war did not find enemy weapons, he wrote.

In 1942, the Navy warned civilians along the Washington and Oregon coasts not to tamper with metal objects washed up on beaches, according to a Seattle Times article from April 1942. While the article states there were no reports of floating enemy mines, the Navy said “watchfulness is the best advice” and advised residents to report sightings.

Roy Ridderbusch, 91, of Lynnwood served two tours of duty with the U.S. Navy at Fort Worden in Port Townsend as an electrician’s mate first class in the 1950s. He worked at the minefield in San Francisco area and then was transferred to Washington to set up a harbor defense unit.

Ridderbusch said there were plans to defend Puget Sound with a minefield, but as far as he knows, the idea was shelved. At that time, he said the military used mines that looked like drums and were around 6 feet in diameter and 4 feet high. They sat on the ocean floor with cables running onto the beach, where an operator could control specific mines “like dialing a telephone.” These didn’t float and weighed about 6,000 pounds, he said.

He said all the mines planted in the Puget Sound region that he saw were for practice and filled with concrete instead of TNT. He recalls exploding one mine during his first tour with the Fort Worden Harbor Entrance Control Post for research. In an interview with the Fort Worden Oral History Program, he said the explosion brought up two sturgeons that were killed by the concussion, but no other wildlife appeared to have been killed.

Sheriff’s Deputy Scott Wilson said Wednesday that the mine’s appearance was a unique occurrence in his 24 years with the agency.

Other incidents of Navy weapons appearing out of nowhere have not been so harmless.

In 1957, a 15-foot Navy torpedo flew out of the water and hit the Bainbridge Island shed of shipyard worker George Munro, the father of then-future Washington Secretary of State Ralph Munro, The Times then reported. The Navy wouldn’t say where the unarmed torpedo was fired from, according to the article, sent to The Times by state research archivist Benjamin Helle.