Cryptonomicon

"Two silver bars, Lawrence, each with a value of some hundred and twenty-five pounds. One of them should be very close to us." Alan stands up, pulls a compass out of his pocket, turns to face magnetic north, and squares his shoulders. Then he rotates a few degrees. "Can't remember whether I allowed for declination," he mumbles. "Right! In any case. One hundred paces north." And he strides off into the woods, followed by Lawrence, who has been given the job of carrying the metal detector.

Just as Dr. Alan Turing can ride a bicycle and carry on a conversation while mentally counting the revolutions of the pedals, he can count paces and talk at the same time too. Unless he has lost count entirely, which seems just as possible.

"If what you are saying is true," Lawrence says, "the jig must be up already. Rudy must have figured out that we've broken their codes."

"An informal system has been in place, which might be thought of as a precursor to Detachment 2701, or 2702 or whatever we are calling it," Alan says. "When we want to sink a convoy, we send out an observation plane first. It is ostensiblyan observation plane. Of course, to observe is not its realduty--we already know exactly where the convoy is. Its realduty is to be observed--that is, to fly close enough to the convoy that it will be noticed by the lookouts on the ships. The ships will then send out a radio message to the effect that they have been sighted by an Allied observation plane. Then, when we come round and sink them, the Germans will not find it suspicious--at least, not quite so monstrously suspicious that we knew exactly where to go.

Alan stops, consults his compass, turns ninety degrees, and begins pacing westwards.

"That strikes me as being a very ad hoc arrangement," Lawrence says. "What is the likelihood that Allied observation planes, sent out purportedly at random, will just happen to notice every single Axis convoy?"

"I've already calculated that probability, and I'll bet you one of my silver bars that Rudy has done it too," Turing says. "It is a very small probability."

"So I was right," Lawrence says, "we have to assume that the jig is up."

"Perhaps not just yet," Alan says. "It has been touch and go. Last week, we sank a convoy in the fog."

"In the fog?"

"It was foggy the whole way. The convoy could not possibly have been observed. The imbeciles sank it anyway. Kesselring became suspicious, as would anyone. So we ginned up a fake message--in a cypher that we know the Nazis have broken--addressed to a fictitious agent in Naples. It congratulated him on betraying that convoy to us. Ever since, the Gestapo have been running rampant on the Naples waterfront, looking for the fellow."

"We dodged a bullet there, I'd say."

"Indeed." Alan stops abruptly, takes the metal detector from Lawrence, and turns it on. He begins to walk slowly across a clearing, sweeping the wire loop back and forth just above the ground. It keeps snagging on branches and getting bent out of shape, necessitating frequent repairs, but remains stubbornly silent the whole time, except when Alan, concerned that it is no longer working, tests it on Lawrence's belt buckle.

"The whole business is delicate," Alan muses. "Some of our SLUs in North Africa--"

"SLUs?"

"Special Liaison Units. The intelligence officers who receive the Ultra information from us, pass it on to field officers, and then make sure it is destroyed. Some of them learned, from Ultra, that there was to be a German air raid during lunch, so they took their helmets to the mess hall. When the air raid came off as scheduled, everyone wanted to know why those SLUs had known to bring their helmets."

"The entire business seems hopeless," Lawrence says. "How can the Germans not realize?"

"It seems that way to us because we know everything and our channels of communication are free from noise," Alan says. "The Germans have fewer, and much noisier, channels. Unless we continue to do stunningly idiotic things like sinking convoys in the fog, they will never receive any clear and unmistakable indications that we have broken Enigma."

"It's funny you should mention Enigma," Lawrence says, "since that is an extremely noisy channel from which we manage to extract vast amounts of useful information."

"Precisely. Precisely why I am worried."

"Well, I'll do my best to spoof Rudy," Waterhouse says.

"You'll do fine. I'm worried about the men who are carrying out the operations."

"Colonel Chattan seems pretty dependable," Waterhouse says, though there's probably no point in continuing to reassure Alan. He's just in a fretting mood. Once every two or three years, Waterhouse does something that is socially deft, and now's the time: he changes the subject: "And meanwhile, you'll be working it out so that Churchill and Roosevelt can have secret telephone conversations?"