Enigma (4 page)

♦

The Germans called it Triton, after the son of Poseidon, the
demigod of the ocean who blew through, a twisted seashell to raise
the furies of the deep. “German humour,” Puck had groaned when they
discovered the code name, “German fucking humour.” But at Bletchley
they stuck to Shark. It was a tradition, and they were British and
they liked their traditions. They named all the enemy’s ciphers
after sea creatures. The main German naval cipher they called
Dolphin. Porpoise was the Enigma key for Mediterranean surface
vessels and shipping in the Black Sea. Oyster was an “officer only”
variation on Dolphin. Winkle was the “officer only” variant of
Porpoise.

And Shark? Shark was the operational cipher of the U-boats.

Shark was unique. Every other cipher was produced on a standard
three-rotor Enigma machine. But Shark came out of an Enigma with a
specially adapted fourth rotor which made it twenty-six times more
difficult to break. Only U-boats were allowed to carry it.

It came into service on 1 February 1942 and it blacked out
Bletchley almost completely.

Jericho remembered the months that followed as a prolonged
nightmare. Before the advent of Shark, the cryptanalysts in Hut 8
had been able to break most U-boat transmissions within a day of
interception, allowing ample time to re-route convoys around the
wolf packs of German submarines. But in the ten months after the
introduction of Shark they read the traffic on just three
occasions, and even then it took them seventeen days each time, so
that the intelligence, when it did arrive, was virtually useless,
was ancient history.

To encourage them in their labours a graph was posted in the
code-breakers’ hut, showing the monthly tonnages of shipping sunk
by the U-boats in the North Atlantic. In January, before the
blackout, the Germans destroyed forty-eight Allied ships. In
February they sank seventy-three. In March, ninety-five. In May,
one hundred and twenty…

“The weight of our failure,” said Skynner, the head of the Naval
Section, in one of his portentous weekly addresses, “is measured in
the bodies of drowned men.”

In September, ninety-five ships were sunk. In November,
ninety-three…

And then came Fasson and Grazier.

♦

Somewhere in the distance the college clock began to toll.
Jericho found himself counting the chimes.

“Are you all right, old thing? You’ve gone terribly silent.”

“Sorry. I was just thinking. Do you remember Fasson and
Grazier?”

“Fasson and who? Sorry, I don’t think I ever met them.”

“No. Nor did I. None of us did.”

♦

Fasson and Grazier. He never knew their Christian names. A first
lieutenant and an able-bodied seaman. Their destroyer had helped
trap a U-boat, the U-459, in the eastern Mediterranean. They had
depth-charged her and forced her to the surface. It was about ten
o’clock at night. A rough sea, a wind blowing up. After the
surviving Germans had abandoned the submarine, the two British
sailors had stripped off and swum out to her, lit by searchlights.
The U-boat was already low in the waves, holed in the conning tower
by cannon fire, shipping water fast. They’d brought off a bundle of
secret papers from the radio room, handing them to a boarding party
in a boat alongside, and had just gone back for the Enigma machine
itself when the U-boat suddenly went bows up and sank. They went
down with her—half a mile down, the Navy man had said when he told
them the story in Hut 8. “Let’s just hope they were dead before
they bit the bottom.”

And then he’d produced the code books. This was on 24 November
1942. More than nine and a half months into the blackout.

At first glance they scarcely looked worth the cost of two men’s
lives: two little pamphlets, the Short Signal Book and the Short
Weather Cipher, printed in soluble ink on pink blotting paper,
designed to be dropped into water by the wireless operator at the
first sign of trouble. But to Bletchley they were beyond price,
worth more than all the sunken treasure ever raised in history.
Jericho knew them by heart even now. He closed his eyes and the
symbols were still there, burned into the back of his retina.

T = Lufttemperatur in ganzen Celsius-Graden.—28C = a.—27C =
b.—26C…

U-boats made daily weather reports: air temperature, barometric
pressure, wind-speed, cloud-cover…

The Short Weather Cipher book reduced that data to a half-dozen
letters. Those half-dozen letters were enciphered on the Enigma.
The message was then broadcast from the submarine in Morse code and
picked up by the German Navy’s coastal weather stations. The
weather stations used the U-boats’ data to compile meteorological
reports of their own. These reports were then re-broadcast, an hour
or two later, in a standard three-rotor Enigma weather cipher—a
cipher Bletchley could break—for the use of every German
vessel.

It was the back door into Shark.

First, you read the weather report. Then you put the weather
report back into the short weather cipher. And what you were left
with, by a process of logical deduction, was the text that had been
fed into the four-rotor Enigma a few hours earlier. It was a
perfect crib. A cryptanalyst’s dream.

But still they couldn’t break it.

Every day the code-breakers, Jericho among them, fed their
possible solutions into the bombes—immense electro-mechanical
computers, each the size of a walk-in wardrobe, which made a noise
like a knitting machine—and waited to be told which guess was
correct. And every day they received no answer. The task was simply
too great. Even a message enciphered on a three-rotor enigma might
take twenty-four hours to decode, as the bombes clattered their way
through the billions of permutations. A four-rotor Enigma,
multiplying the numbers by a factor of twenty-six, would
theoretically take the best part of a month.

For three weeks Jericho worked round the clock, and when he did
grab an hour or two’s sleep it was only to dream fitfully of
drowning men. “Let’s just hope they were dead before they hit the
bottom…” His brain was beyond tiredness. It ached physically, like
an overworked muscle. He began to suffer blackouts. These only
lasted a matter of seconds but they were frightening enough. One
moment he might be working in the Hut, bent over his slide-rule,
and the next everything around him had blurred and jumped on, as if
a film had slipped its sprockets in a projector. He managed to beg
some Benzedrine off the camp doctor but that only made his mood
swings worse, his frenzied highs followed by increasingly
protracted lows.

Curiously enough, the solution, when it came, had nothing to do
with mathematics, and afterwards he was to reproach himself
furiously for becoming too immersed in detail. If he had not been
so tired, he might have stepped back and seen it earlier.

It was a Saturday night, the second Saturday in December. At
about nine o’clock Logie had sent him home. Jericho had tried to
argue, but Logie had said: “No, you’re going to kill yourself if
you go on at this rate, and that won’t be any use to anyone, old
love, especially you.” So Jericho had cycled wearily back to his
digs above the pub in Shenley Church End and had crawled beneath
the bedclothes. He heard last orders called downstairs, listened as
the final few regulars departed and the bar was closed up. In the
dead hours after midnight he lay looking at the ceiling wondering
if he would ever sleep again, his mind churning like a piece of
machinery he couldn’t switch off.

It had been obvious from the moment Shark had first surfaced
that the only acceptable, long-term solution was to redesign the
bombes to take account of the fourth rotor. But that was proving a
nightmarishly slow process. If only they could somehow complete the
mission Fasson and Grazier had begun so heroically and steal a
Shark Enigma. That would make the redesign easier. But Shark
Enigmas were the crown jewels of the German Navy. Only the U-boats
had them. Only the U-boats and, of course, U-boat communication
headquarters in Sainte-Assise, southeast of Paris.

A commando raid on Sainte-Assise, perhaps? A parachute drop? He
played with the image for a moment and then dismissed it.
Impossible. And, in any case, useless. Even if, by some miracle,
they got away with a machine, the Germans would know about it, and
switch to a different system of communications. Bletchley’s future
rested on the Germans continuing to believe that Enigma was
impregnable. Nothing could ever be done which might jeopardise that
confidence. Wait a minute. Jericho sat upright. Wait a bloody
minute.

If only the U-boats and their controllers in Saint-Assise were
allowed to have four-rotor Enigmas—and Bletchley knew for a fact
that that was the case—how the hell were the coastal weather
stations deciphering the U-boat’s transmissions?

It was a question no one had bothered to stop and ask, yet it
was fundamental.

To read a message enciphered on a four-rotor machine you had to
have a four-rotor machine.

Or did you?

If it is true, as someone once said, that genius is “a zigzag of
lightning across the brain”, then, in that instant, Jericho knew
what genius was. He saw the solution lit up like a landscape before
him.

He seized his dressing gown and pulled it over his pyjamas. He
grabbed his overcoat, his scarf, his socks and his boots and in
less than a minute he was on his bike, wobbling down the moonlit
country lane towards the Park. The stars were bright, the ground
was iron-hard with frost. He felt absurdly euphoric, laughing like
a madman, steering directly into the frozen puddles along the edge
of the road, the ice crusts rupturing under his tyres like drum
skins. Down the hill he freewheeled into Bletchley. The countryside
fell away and the town spread out beneath him in the moonlight,
familiarly drab and ugly but on this night beautiful, as beautiful
as Prague or Paris, perched on either bank of a gleaming river of
railway tracks. In the still air he could hear a train half a mile
away being shunted in the sidings—the sudden, frantic chugging of a
locomotive followed by a series of clanks, then a long exhalation
of steam. A dog barked and set off another. He passed the church
and the war memorial, braked to avoid skidding on the ice, and
turned left into Wilton Avenue.

He was panting with exertion by the time he reached the Hut,
fifteen minutes later, so much so he could barely blurt out his
discovery and catch his breath and stop himself from laughing at
the same time:
“—They’re—using—it—as—a—three-rotor—machine—they’re—leaving—the—fourth—rotor—in—neutral—when—they—do—the—weather—stuff—the—silly—bloody—buggers—”

His arrival caused a commotion. The night shift all stopped
working and gathered in a concerned half-circle round him—he
remembered Logie, Kingcome, Puck and Proudfoot—and it was clear
from their expressions they thought he really had gone mad. They
sat him down and gave him a mug of tea and told him to take it
again, slowly, from the beginning.

He went through it once more, step by step, suddenly anxious
there might be a flaw in his logic. Four-rotor Enigmas were
restricted to U-boats and Sainte-Assise: correct? Correct.
Therefore, coastal stations could only decipher three-rotor Enigma
messages: correct? Pause. Correct. Therefore, when the U-boats sent
their weather reports, the wireless operators must logically
disengage the fourth rotor, probably by setting it at zero.

After that, everything happened quickly. Puck ran along the
corridor to the Big Room and laid out the best of the weather cribs
on one of the trestle tables. By 4 A.M. they had a menu for the
bombes. By breakfast one of the bombe bays was reporting a drop and
Puck ran through the canteen like a schoolboy shouting: “It’s out!
It’s out!”

It was the stuff of legend.

At midday Logie telephoned the Admiralty and told the Submarine
Tracking Room to stand by. Two hours later, they broke the Shark
traffic for the previous Monday and the Teleprincesses, the
gorgeous girls in the Teleprinter Room, began sending the
translated decrypts down the line to London. They were indeed the
crown jewels. Messages to raise the hairs on the back of your
neck.

FROM: U-BOAT TO CAPTAIN SCHRODER

FORCED TO SUBMERGE BY DESTROYERS. NO CONTACT.
LAST POSITION OF ENEMY AT 0815 NAVAL GRID SQUARE 1849.

COURSE 45 DEGREES, SPEED 9 KNOTS.

FROM: GILADORNE

HAVE ATTACKED. CORRECT POSITION OF CONVOY IS
AK1984. 050 DEGREES. AM RELOADING AND KEEPING CONTACT.

FROM: HAUSE

AT 0115 IN SQUARE 3969 ATTACKED, FLARES AND
GUNFIRE, DIVED, DEPTH CHARGES. NO DAMAGE. AM IN NAVAL GRID SQUARE
AJ3996. ALL TIN FISH, 70 CBM.

FROM: FLAG OFFICER, U-BOATS

TO: “DRAUFGANGER” WOLF PACK

TOMORROW AT 1700 BE IN NEW PATROL LINE FROM
NAVAL GRID SQUARE AK2564 TO 2994. OPERATIONS AGAINST EASTBOUND
CONVOY WHICH AT 1200⁄7⁄12 WAS IN NAVAL GRID SQUARE AK4189. COURSE
050 TO 070 DEGREES. SPEED APPROX 8 KNOTS.

By midnight they had broken, translated and teleprintered to
London ninety-two Shark signals giving the Admiralty the
approximate whereabouts and tactics of half the Germans’ U-boat
fleet.

Jericho was in the Bombe Hut when Logie found him. He had been
chasing about for the best part of nine hours and now he was
supervising a changeover on one of the machines, still wearing his
pyjamas under his overcoat, to the great amusement of the Wrens who
tended the bombe. Logie clasped Jericho’s hand in both of his and
shook it vigorously.

“The Prime Minister!” he shouted in Jericho’s ear, above the
clattering of the bombes.