8 September 2009
Deperming is a procedure for erasing the permanent magnetism from ships and
submarines to camouflage them against magnetic detection vessels and enemy
A sea-going metal-hulled ship or submarine, by its very nature, develops
a magnetic signature as it travels due to a magneto-mechanical interaction
with the Earth's magnetic field. This signature can be exploited by magnetic
mines, or facilitate the detection of a submarine by ships or aircraft with
magnetic anomaly detection (MAD) equipment. Navies use the deperming procedure,
in conjunction with degaussing, as a countermeasure against this.
Specialized deperming facilities, such as the United States Navy's Lambert's
Point Deperming Station are used to perform the procedure. Heavy gauge copper
cables are wrapped around the hull and superstructure of the vessel, and
very high electrical currents (as high as 4000 amps) are pulsed through the
cables. This has the effect of "resetting" the ship's magnetic signature.
It is also possible to assign a specific signature that is best suited to
the particular area of the world the ship will operate in. Over time the
deperm will begin to degrade and the procedure must be redone periodically
to maintain the desired effect.
deperm-eyeball.htm Submarine Magnetic Silencing Facilities August 18, 2006
RELEASE No. 690-09
September 08, 2009
Navy Announces Decision on Norfolk Harbor Channel Dredging
The Navy announced today its decision to deepen approximately five miles
of the Norfolk Harbor Channel in the Elizabeth River. This action will allow
the continuous safe and expeditious travel of aircraft carriers to and from
the Norfolk Naval Shipyard (NNSY) and the Lamberts Point Deperming Station.
Dredging this heavily-used waterway, which is the federal navigation channel
within the Elizabeth River in Norfolk, Portsmouth, and Chesapeake, would
occur from the Lamberts Point Deperming Station in the Lamberts Bend Reach,
south to NNSY in the Lower Reach. Dredging would occur completely within
the existing Army Corps of Engineers-maintained federal navigation channel.
The action is necessary because currently there is not enough space between
the keel of transiting aircraft carriers and the bottom of the channel. This
causes mud and other debris from the river bottom to be drawn into the engine
cooling and firefighting systems, creating the potential for engine damage,
costly delays, and unsafe conditions.
To avoid these conditions, aircraft carrier movements into and out of the
deperming station and NNSY are now limited to high tide periods. These conditions
must be alleviated in order for the Navy to meet the requirement of maintaining
the combat readiness of its nuclear-powered aircraft carriers, and effectively
and efficiently perform its national defense mission.
The Navy's decision conforms to the process outlined in the National
Environmental Protection Act, which requires analysis of the environmental
consequences of federal actions. The Navy consulted with state and federal
regulatory agencies throughout the environmental impact statement (EIS) process,
including the U.S. Fish and Wildlife Service, the National Marine Fisheries
Service, the Virginia Department of Environmental Quality, and the Virginia
Department of Historic Resources. The U.S. Army Corps of Engineers was a
cooperating agency in this EIS.
The record of decision is available on the project Web site at
http://www.norfolkdredgingeis.com . For further information, contact Navy
Public Affairs at 703-697-5342.