A few minutes after midnight she heard a burst of Morse in a fist she did not recognize. The cadence was poor, the pace slow and uncertain. An amateur, she thought, someone who didn't use their radio much. Certainly not one of the professionals at BdU, the Kriegsmarine headquarters. Acting quickly, she made a recording of the transmission on the oscillograph--a device that would in effect create a radio fingerprint of the signal called a Tina--and furiously scribbled the Morse message onto a sheet of paper. When the amateur finished, Charlotte heard another burst of code on the same frequency. This was no amateur; Charlotte and the other Wrens had heard him before. They had nicknamed him Fritz. He was a radio operator aboard a U-boat. Charlotte quickly transcribed this message as well.
Fritz's transmission was followed by another burst of sloppy Morse by the amateur, and then the communication went dead. Charlotte removed her headset, tore off the printout of the oscillograph, and marched across the room. Normally she would simply pass on the Morse transcripts of the messages to the motorcycle courier, who in turn would rush them to Bletchley Park for decoding. But there was something different about this communication--she could feel it in the fist of the radio operators: Fritz aboard a U-boat, an amateur somewhere else. She suspected she knew what it was, but she would have to make a damned convincing case. She presented herself to the night supervisor, a pale exhausted-looking man called Lowe. She dropped the transcripts and the oscillograph on his desk. He looked up at her, a quizzical expression on his face.
"I could be completely wrong, sir," Charlotte said, mustering the most authoritative voice she could, "but I think I just overheard a German spy signaling a U-boat off the coast."
Kapitanleutnant Max Hoffman would never get used to the stench of a U-boat that has been submerged too long: sweat, urine, diesel oil, potatoes, semen. The assault on his nostrils was so intense he would gladly stand watch on the conning tower in a gale rather than stay inside.
Standing in the control room of U-509, he could feel the throb of its electric motors beneath his feet as they wheeled in a monotonous circle twenty miles from the British coastline. A fine mist hung inside the submarine, creating a halo around every light. Every surface was cool and wet to the touch. Hoffman liked to imagine it was dew on a spring morning, but one look at the cramped claustrophobic world he inhabited robbed him of that fantasy very quickly.
It was a tedious assignment, sitting off the coast of Britain for weeks on end, waiting for one of Canaris's spies. Of Hoffman's crew only his first officer knew the true purpose of their mission. The rest of the men probably suspected as much, since they weren't on patrol. Still, things could be worse. Given the extraordinary loss rate among the Ubootwaffe--nearly 90 percent--Hoffman and his crew were damned lucky to have survived this long.
The first officer came onto the bridge, face grave, a sheet of paper in his hand. Hoffman looked at the man, depressed by the notion that he probably looked just as bad: sunken eyes, hollow cheeks, the gray pallor of a submariner, the unkempt beard because there was too little fresh water to waste on shaving.
The first officer said, "Our man in Britain has finally surfaced. He'd like a lift home tonight."
Hoffman smiled, thinking, Finally. We pick him up and head back to France for some good food and clean sheets. He said, "What's the latest weather?"
"Not good, Herr Kaleu," the first officer said, using the customary diminutive form of kapitanleutnant. "Heavy rains, winds thirty miles per hour from the northwest, seas ten to twelve."
"Jesus Christ! And he'll probably be coming in a rowboat--if we're lucky. Organize a reception party and prepare to surface. Have the radio operator inform BdU of our plans. Set a course for the rendezvous point. I'll go up top with the lookouts. I don't care how bad the weather is." Hoffman made a face. "I can't stand the fucking smell in here any longer."
"Yes, Herr Kaleu."
The first officer shouted a series of commands, echoed among the crew. Two minutes later, U-509 punched through the stormy surface of the North Sea.
The system was known as High Frequency Direction Finding, but almost everyone involved with the project knew it as Huff Duff. It worked on the principle of triangulation. The radio fingerprint created by the oscillograph at Scarborough could be used to identify the type of transmitter and its power supply. If the Y Service stations at Flowerdown and Iceland also ran oscillographs, the three recordings could be used to establish bearing lines--known as cuts--which could then be used to locate the position of the transmitter. Sometimes Huff Duff could pinpoint a radio to within ten miles of its geographical location. Usually, the system was much less accurate, thirty to fifty miles.
Commander Lowe did not believe Charlotte Endicott was completely wrong. In fact, he believed she had stumbled onto something critical. Earlier that evening, a Major Vicary from MI5 had sent out an alert to the Y Service to look for this very sort of thing.
Lowe spent the next few minutes speaking with his counterparts in Flowerdown and Iceland, attempting to plot a fix on the transmitter. Unfortunately, the communication was short, the fix not terribly precise. In fact, Lowe could narrow it only to a rather large portion of eastern England--all of Norfolk and much of Suffolk, Cambridgeshire, and Lincolnshire. Probably not much of a help, but at least it was something.
Lowe dug through the papers on his desk until he found Vicary's number in London and then reached for his secure telephone.