Path: utzoo!attcan!uunet!samsung!brutus.cs.uiuc.edu!psuvax1!rutgers!att!cbnews!military
From: pierson@cimnet.dec.com
Newsgroups: sci.military
Subject: Re: Mines
Message-ID: <11601@cbnews.ATT.COM>
Date: 21 Nov 89 04:20:42 GMT
Sender: military@cbnews.ATT.COM
Organization: Digital Equipment Corporation
Lines: 42
Approved: military@att.att.com



From: pierson@cimnet.dec.com


In article <11549@cbnews.ATT.COM>, entropy@pawl.rpi.edu (Mark-Jason Dominus)
writes, in part:
..
> 
>What is a magnetic mine?  How does it work?
> 

A (sub sea) mine triggered by a change in the local magnetic field, assumed to
be caused by a large mass of metal (a ship...) passing by.  Initial units used
(basically) a delicately balanced compass needle, free to swing on all axes. 
When it swung, it closed contacts to an electrically fused primer.  Current
ones are presumably more sophisticated.

Until understood, hard to sweep.  Later swept by wooden hulled ships, and low
flying aircraft fitted with large electromagnets.  Also "defeated" by
degaussing (demagnetizing) the ships expecting to pass near such mines.
Still in use.

Another advantage is that they can't be swept by towed paravane gear.
Also, can be laid in shallower water than tethered contact mines.  

Other mine fusing schemes:

	Contact:	Traditional, requires mine to be close enough to
	surface for ship to hit it.

	Observation/Controlled:	Earliest.  Shore station fires mine when
	target ship is over it.  Useful for coast defense.

	Sonic/Acoustic	Triggered by waterborne sound

Thanks
dave pierson			|The facts, as accurately as i can manage,
Digital Equipment Corporation	|The opinions, my own.
600 Nickerson Rd
Marlboro, Mass
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