Navy pursuing new submarine signature range

The Navy wants to build a range in Hood Canal to measure the electromagnetic signatures of 13 Kitsap-based submarines, which now must transit two weeks to Pearl Harbor or San Diego for the five-minute job.

Submarines develop a magnetic signature as they travel because of a magneto-mechanical interaction with the Earth's magnetic field. The signature can be exploited by magnetic mines, or detected by specially equipped ships and aircraft.

Naval Base Kitsap-Bangor used to have a range, but when civilian boating increased in the 1990s, it was closed for safety concerns. The sensors, at 150 feet, were also too deep. Submarines had to dive to periscope depth to use them, requiring Coast Guard escorts to clear and keep other boats out of the area for relatively long periods of time, according to a Navy document. A temporary electromagnetic measurement range was installed in 2000, but ceased operation after being damaged by the anchor of a commercial fishing vessel in 2007.

The Navy says the range needs to be within a half mile of the submarines' transit route and within 1.5 miles of a submarine homeport. Ideally, the homeport would already have a shore facility available. The range would be no more than a mile from shore in about 70 feet of water, away from shipping routes and strong currents.

The proposed location is just north of the Bangor base in Hood Canal Military Operating Area North, according to the draft report. The facility would comprise a sensor array system with 21 sensors spread across 400 feet and buried at the bottom of the canal. There would be an offshore 15 foot by 15 foot platform requiring five 24-inch square concrete piles. About 8,500 feet of composite cable connecting the sensors would also be buried, using a horizontal directional drilling jet plow.

Construction would occur between July 15, 2014, and Oct. 1, 2014. Cost estimates aren't available.

A submarine, escorted by the Coast Guard, would travel at about 10 knots at the water's surface. The boats take a brief detour from the usual route to go over the sensor array system. The sensors would measure the sub's electromagnetic signature and transfer it to the onshore facility. The whole process would take about five minutes.