A proper law

[David Hansen]

On 6 Mar 2003 at 13:48, Ian G Batten wrote:

> To me, far more interesting are the breaks into Fish and Tunny, which
> on the face of it are fairly strong systems.

I was actually thinking of such things, but only mentioned Enigma.

My recollection is that Tunny was a British machine, made out of 
standard Post Office equipment, that replicated one of two German 
machines. ISTR the British name Fish covered the whole system.

My recollection is that the initial British break came about because 
it was used badly as well. A clerk sent identical messages using two 
different settings (due to a garble at the far end). Do some simple 
mathematics and one gets some very interesting information due to the 
nature of the addition used in the machine. Spend months studying 
this and one can reconstruct the complete machine. I recollect that 
Bletchley Park never actually saw the machine they were breaking 
until near the end/after the war. They had however seen similar 
machines made by a different company and all sides are generally 
aware of what is possible. Even managing to intercept the signals was 
difficult, let alone decrypting them.

Part of the trouble with these machines was the way the key was 
"entered". It took considerable time for the cipher clerk to set up 
all the little swinging pins on all the wheels. This made them not 
keen to change settings too often. It would have been better had the 
Germans devised some way of programming the key, though this was 
probably impossible on a machine with mechanical wheels and swinging 
arms. I gather thet the Tunny could be set up with any key, by 
plugging standard exchange plugs into the settings for each wheel and 
then driving it forward till the electro-mechanical "wheels" were at 
the same settings. Luxury.

> > It's hard to
> > remember now that there were once educated people who thought the
> > movement faster than the speed of sound would be impossible.
> 
> I didn't know that that theory was advanced.

I think it was, for large objects like aeroplanes.

True story. The only thing to properly penetrate German U-Boat pens 
was a rocket propelled bomb devised by the Royal Navy, which was only 
used a handful of times. The RAF were very unhappy at the RN 
designing anything to do with aeroplanes and one of their objections 
was that the bomb would have to travel faster than the speed of sound 
to penetrate and this was hard/impossible. To this the RN replied 
that they had many years of dealing with supersonic projectiles, so 
the speed was no problem for their people. IIRC the RAF (well Barnes 
Wallace actually) did eventually come up with a bomb that travelled 
at around/possibly just above the speed of sound, though not as fast 
as the RN bomb.

> > Or, even earlier, that travel faster than 45 mph
> > would be impossible to sustain as the change in air pressure would
> > cause the suffocation of any who tried.
> 
> That's close to an urban myth.  It's alternatively said that the man
> who advanced that theory was regarded as a nutcase even at the time,
> or that it was never advanced in a spirit beyond that of satire.

My recollection is that he claimed that if the brakes of a train 
failed as it entered Box Tunnel the train would emerge at 120mph, at 
which speed nobody onboard would be able to breathe. I assume the 
assumption was of a train entering the tunnel at 60mph, broad gauge 
trains travelled very fast compared to their narrow gauge sisters at 
the time.

Brunel pointed out that he had forgotton the "minor" matter of air 
resistance. Anyway we now know people can breathe at such speeds, 
though the air is rather solid in feel.

The man was regarded as a dangerous nutcase at the time, by those 
with responsibility for operating trains safely. Unfortunately others 
regarded him as an expert, with the result that he was allowed to run 
an "experimetal train" around the GWR system wherever and whenever 
the fancy took him, much to the consternation of those trying to run 
a service and to the danger of staff and passengers on those 
services.


--
  David Hansen, Edinburgh | PGP email preferred-key number F566DA0E
 I will *always* explain why I revoke a key, unless the UK 
 government prevents me using the RIP Act 2000.