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From: budden@manta.nosc.mil (Rex A. Buddenberg)
Newsgroups: sci.military
Subject: Mines
Message-ID: <11599@cbnews.ATT.COM>
Date: 21 Nov 89 04:20:35 GMT
Sender: military@cbnews.ATT.COM
Organization: Naval Ocean Systems Center, San Diego
Lines: 29
Approved: military@att.att.com



From: budden@manta.nosc.mil (Rex A. Buddenberg)

Mark-Jason,

A magnetic mine is one that contains a magnetometer (like you
pocket compass, except when the needle moves it closes the firing
circuit) that detects the magnetic signature of a passing ship.
These mines, and magnetically exploded torpedos, were state
of the art at the beginning of WWII.

Other actuating mechanisms (for both mines and torpedoes) include:
  contact -- hull hitting the mine explodes it.  See Iran Ajr in 
Persion Gulf along with USS Roberts.
  acoustic -- listens for propellor noises -- can be quite discriminating
in telling the difference between different kinds of ships.
  pressure -- passing ships create pressure waves, like air pressure
on your eardrums creating sound.
  various timing and remote control mechanisms.

Minesweeping consists of simulating these signatures without actually
hazarding the ships that normally make said signatures.  So mines
have gotten more intelligent over time -- it's hard to fake more
than one of these signatures at a time.  Controllers also have
counters so that x ships pass over the top until everybody is sure
the minefield has been cleared...then whammo.

Rex Buddenberg