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In article <10090@pt.cs.cmu.edu>, rwb@vi.ri.cmu.edu (Bob Berger) writes:
> > In WW II, the Germans installed radar detectors on U-boats.  These 
> > also had a problem with local-oscillator radiation, and Allied ASW 
> > aircraft were able to home-in on them without radar.
> 
> The above statement is NOT true. The mistake is understandable, however,
> because the above statement is EXACTLY what a captured British navigator said
> when his German captors asked how the submarines were being found.
> 
> What was really happening is the British were using a new X band radar
> which was beyond the frequency coverage of the German radar detectors. The
> story about local oscillator leakage was deliberate disinformation.

	The true story is even more interesting than the above, as related
in the "Wizard War" by R. V. Jones (a PhD physicist who eventually headed
the British scientific intelligence effort during World War II).

	The British has *two* means of locating the German U-boats: (1)
the centimeter wavelength "H2S" radar set; and (2) decoded Enigma
messages.  The German Naval Enigma crypto machines contained a 4th
rotor, making it an even more secure code - which was still broken by
the "Colossus" computer at Bletchley Park.

	Of the above two methods, safeguarding the knowledge of the
compromised Enigma machines was by far the more important item.

	Consequently, the British adopted *two* misinformation schemes,
both of which were successful:

1.	Planting the story that LO radiation from the U-boat "Metox"
	countermeasure receiver was the basis for the U-boat location.
	The truth is that the Metox receiver *did* leak LO radiation,
	and the Germans went to some significant effort to reduce it.

2.	Planting the story that the U-boats were located by infrared
	searchlights and imaging apparatus.  The Germans went to an
	amazing effort to develop a composite paint using a glass bead
	coating which not only provided visual camouflage, but infrared
	as well.

	The Germans were amazed that both of the above measures had no
appreciable effect on reducing U-boat losses.  They finally chalked it
off to the centimeter wavelngth radar, never guessing that the compromised
Enigma cipher was equally to blame.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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