Seizing the Enigma (46 page)

Ahead of that convoy, perhaps half a dozen others were crossing the Atlantic in one direction or the other. To sink their ships Dönitz, had, on April 16, sixty-three boats operating in the Atlantic north of Halifax’s latitude of 44° 38′ north. One of the convoys U-Boat
Command was concentrating on was SC 127’s predecessor, SC 126. A report by the B-Dienst told the command that four days previously SC 126 was located some 600 miles southeast of Cape Race, the southern tip of Newfoundland. The convoy had presumably passed the patrol line formed by a wolfpack codenamed
TITMOUSE
. But the submarines’ surface speed was superior to that of most convoys (a U-boat could cover 320 miles in 24 hours, an average convoy 240), so in hope of catching the convoy, Dönitz stretched
TITMOUSE
into a 650-mile northwest-southeast line with the U-boats moving roughly northeast. The next day, however, he abandoned hope of catching SC 126, saying that it might have slipped through the patrol line because of poor visibility.

U-Boat Command knew the rhythm of the convoys, and it knew that they sought to go around the U-boat concentrations. So on the seventeenth, with visibility expected to improve, Dönitz added more submarines to
TITMOUSE
and, supposing that the next convoys from Nova Scotia would go north to avoid wolfpacks, ordered it to take up a new patrol line. Farther west than the previous line, it was intended to catch the Allied ships as they sailed parallel to the Labrador coast.

The next day, however, two U-boats not in
TITMOUSE
spotted a pair of convoys so far to the south that the
TITMOUSE
submarines could not find them. Despite these sightings, U-Boat Command clung to its view that the next convoys would take the northern route. Perhaps reinforcing its belief was a report of a submarine’s sighting, to the north, a convoy that radio intelligence promptly identified as HX 234, from New York.

While U-Boat Command was mulling this over, SC 127 marched at about 7 knots along its predetermined course, passing Points C, D, and E as it headed first southeast out of Halifax and then east. Upon reaching E, at 6
P.M.
Sunday, the eighteenth, it turned onto a course of 66°, or east-northeast. The barometer was now falling and the sky had clouded over, but the sea remained smooth and the air calm. Allied cryptanalysts had solved that day U-Boat Command’s long
two-part message of the seventeenth establishing
TITMOUSE
, which ordered twenty-six submarines to form a patrol line as of 8
A.M.
April 19, listing them in the order in which they were to take up position. Though the U-boats were identified only by their skippers’ names, their numbers were known. The German naval grid positions for the five points through which the line was to run were enciphered, but the cryptanalysts had determined the true meanings of many of the enciphered grid bigrams as well as of the disguised grid four-digit groups. They had learned, for example, that VD 0798 (the northwesternmost point) stood for AJ 5798, or 53° 45′ north, 46° 15′ west and that BU 8641 (the southeasternmost point) was BC 3641, or 49° 45′ north, 39° 55′ west. The solution revealed that the U-boats were to stay 15 miles apart and were to maintain radio silence “except for reports of tactical importance.” And, in a warning ominous to the Allies, it stated: “A convoy headed northeast is expected from that time on”—meaning from the time of the setting up of
TITMOUSE
.

The watch officers transmitted the first part of the solved, translated, and edited intercept to F-21, the Atlantic intelligence section of the headquarters of the U.S. Fleet, at 9:55
P.M.
on Sunday, April 18, and the second part eight hours later, at 5:50
A.M.
the next morning. Later on Monday Cominch—the commander in chief, U.S. Fleet—issued his submarine estimate for April 19. It named sightings, attacks, and direction-finding as sources; cryptanalysis was not cited, though much of the report was based on Enigma solutions. But Cominch blurred the precision that cryptanalysis provided, in part to conceal it as a source but in part because the U-boats might have moved since they received the intercepted orders and might have erred in their own positions and because Cominch did not want convoys and escorts not in the immediate area to relax their guard.

Part 3 of the estimate’s six geographical parts dealt with the North Atlantic. It began: “Twenty to thirty [U-boats] estimated patrolling general area 49-00 to 54-00 [north] and 38-00 to 48-00 [west] from light DF activity.” This was clearly based on the solution of the long
message of April 17. It drew a rectangle based on the patrol line as its diagonal and fudged the number of U-boats. The rest of Part 3 gave details about other subs.

All day Monday, SC 127 followed the same northeast course in cloudy but calm weather. During the morning a patrolling Catalina seaplane made a welcome appearance overhead.

In Washington and Bletchley, the cryptanalysts hit a snag. They were unable to find any cribs, unable to create any usable menus, and so unable to recover the naval Enigma keys for that day. No messages enciphered with the keys of April 19 could be read. As a consequence, the U-boat situation report for Tuesday, April 20, merely repeated the most critical information from the nineteenth: the large rectangle containing the U-boats remained the same, though the number of U-boats reported in it came into focus: twenty-five. Other details changed slightly. For example, the “Four [in] general area 60-00 24-00” of the April 19 report became “About four within 150 miles of 59-00 from numerous DFs” in the April 20 report. This information was available to the Tenth Fleet’s Convoy and Routing Section, which digested it.

Germany’s naval codebreakers were more successful at that moment than the Allies’. They solved a message Tuesday that revealed that on Saturday convoy HX 234, then south of Cape Race, had been rerouted sharply to the north, probably to avoid a concentration of submarines. To counter this, U-Boat Command on Tuesday ordered
TITMOUSE
to move a second time: to the north and slightly west, to block the likely new route of HX 234.

The B-Dienst also solved an intercept dealing with SC 127. This convoy had been placidly plowing the calm western Atlantic on its east-northeast course, and continued to do so on Tuesday, when, at 9:55
A.M.
, a British escort relieved the Canadians. The German solution placed the convoy southeast of Cape Race at 5
P.M.
Tuesday. “Since this position lies relatively far to the south,” U-Boat Command stated, “it is assumed that the convoy, contrary to earlier experience, will keep on the previously steered easterly course.” The command detached four
boats from
TITMOUSE
to set up a short north-south patrol line, to be expanded by submarines coming from the east. The position of the line showed that the Germans expected SC 127 to steam south of the concentration of U-boats they knew the Allies knew about.

That Tuesday, April 20, Adolf Hitler celebrated his fifty-fourth birthday. Before and after it he received the leaders of his cobelligerents in Klessheim castle in Salzburg. On the battlefronts, little of note was happening. Army Group Africa, squeezed into a corner of Tunisia, struck out with a counterattack to throw British preparations for an assault off balance. In the air, the British bombed Stettin, a Baltic port, with 304 planes; the Soviets likewise attacked Tilsit, farther east. The Jews in the Warsaw ghetto were in the second day of their heroic uprising. In Germany, people were talking about the discovery of the mass grave in Katyn of more than 10,000 Polish officers murdered by the Soviets. Some saw it as an example of what awaited the Germans if the Russians won the war; others said the Germans had no right to criticize since they had killed Jews and Poles in much greater numbers. Of the war situation, Germans said realistically that they were powerless in the air and that a German Dunkirk was approaching in Tunisia. Some wanted Hitler to show himself more, at least in newspaper photos and newsreels, to prove that his hair had not turned white. But any despair they felt was not translated into a slowdown at work: production of guns, planes, U-boats climbed.

In the United States, the baseball season opened. Since President Roosevelt was away—meeting the president of Mexico in Monterrey and pledging to beat the Axis so that the Good Neighbor policy could be extended throughout the world—the first ball was thrown out by Paul V. McNutt, the manpower commissioner. A crowd sprinkled with khaki and blue watched the Washington Senators beat the Philadelphia Athletics, 7–5. New York Mayor Fiorello La Guardia announced that 625 summonses had been served on retail food stores for violating food price ceilings and rationing regulations. In Tampa
eight men and a cat came ashore in a life raft after their ship sank in the Gulf of Mexico.

And in the huge room of the Tenth Fleet’s Convoy and Routing Section in Washington, and in the staff rooms of the U-Boat Command in Berlin, men in blue uniforms pored over their vast lined charts of the North Atlantic, playing their deadly games of nautical chess, seeking, with the help of the totality of their knowledge, to outthink the other side and moving their vessels to destroy as many of the enemy’s or save as many of their own as possible. On April 20, the naval officers in Washington, including blond Lieutenant Commander Rollo N. Norgaard, who shared responsibility for SC 127, outthought—either by luck or by design—the officers in Berlin. They sent SC 127 not to the south of the big rectangle in the west central Atlantic that had held the
TITMOUSE
submarines, as U-Boat Command expected, but west and north of it. At 1539 hours Greenwich mean time, they released the first part and, five minutes later, the second part of a message to the warships escorting SC 127.

The convoy was then heading east-northeast to Point F, where it was to turn northeast to Point G—a route that would have taken it directly through the concentration of U-boats. The message told it to head instead for a new point, WL, at 50° north, 50° west. After that it was to steer due north to WM, at 55° north, 50° west, and then east-northeast to WN, east-southeast of Cape Farewell, the southern tip of Greenland. This diversion would take it around the U-boats, leaving them to the east and south. When it received this message, the convoy had passed the 50th meridian; to get to WL, it had to backtrack a little. At 1850 Greenwich mean time, the commodore, van den Donker, altered course. The officers of Convoy and Routing had made an important move in the game.

U-Boat Command continued to seek the convoy to the south. On Wednesday, April 21, it ordered the formation of a new wolf pack,
WOODPECKER
, for the boats detached from
TITMOUSE
and for more than a dozen others recently refueled by the tanker U-487. By noon
the next day,
WOODPECKER
was to stretch some 300 miles north and south. The convoy was expected a few hours before the formation was complete, but surfaced U-boats could easily catch the convoy even if it arrived early. To prevent the Allies from learning of
WOODPECKER
and so possibly diverting SC 127, the U-boats were instructed to maintain radio silence until contact reports had to be made.

While
WOODPECKER
was forming, one of
TITMOUSE
’s northernmost boats, the U-306, spotted the New York convoy HX 234. At 1:55
A.M.
on Thursday, the U-306 torpedoed a 10,000-ton Danish freighter, the
Amerika
. Soon seven and eventually twenty-one
TITMOUSE
boats were operating against HX 234. This drew them away from SC 127, whose new route would have taken it almost through the center of the
TITMOUSE
patrol line.

SC 127 was, however, having troubles of its own. On Wednesday morning, the third ship in the fifth column reported seeing a periscope between herself and the sixth column. The escort leader attacked with a pattern of fourteen depth charges what he thought was “a very doubtful contact”; he concluded that it was a false alarm. Immediately thereafter, the convoy, on its new, backtracking northwest course, spotted ice. One of the escorts thought the convoy could get through the loose pack and bergs and accompanied it; the escort commander followed a lead in another direction but could see no open water. He finally asked van den Donker to steer due east to work around the ice. The convoy had to turn around in a 4- to 6-mile gap in the ice, which the commodore and the other masters accomplished with great skill.

But the escort commander, Lieutenant Commander C. E. Bridgeman, Royal Naval Reserve, could see that heading east would send the convoy right toward the area that the new course was intended to avoid. Instructed to head north, not east, he wanted to gain ground to the north by going northeast, and felt that the bright moon and good visibility would limit the danger from the ice. So after several hours of steaming east, he altered to the northeasterly course,
sending one of the escorts ahead as an ice patrol; it stood by one berg with dimmed lights as the convoy paraded slowly by. During the night, the growlers and bergs thinned out, and early in the morning of Thursday the twenty-second, Bridgeman thought it safe to return to the original northwest course, which the convoy soon did.

By then the Allies had resumed solving German U-boat messages. But they were not quite current: messages of the twentieth and the twenty-first were being sent to Knowles’s Submarine Tracking Room on the twenty-second. One of the solutions perhaps elicited some satisfaction among Norgaard and the others who had diverted SC 127. U-Boat Command had told
WOODPECKER
that an eastbound convoy was expected on April 22 in the approximate latitude of naval grid square BC 69, which would put it almost in the middle of the
WOODPECKER
line, an ideal location for a wolfpack attack. This was SC 127’s original route, now changed; the solution confirmed that Convoy and Routing’s diversion of SC 127 to the north had been wise.

The intercepted German messages were reflected in Cominch’s U-boat estimates. The estimate for the twenty-first shrank the big rectangle in the west central Atlantic both in size and in number of U-boats and added two other infested areas halfway between Newfoundland and Greenland: “About ten [U-boats] estimated within 150 miles 56-00 46-00 from numerous DFs indicating probability that both HX 234 and ON 178 are being shadowed X Several within 150 miles of 54-00 50-00 from recent DFs possibly shadowing ONS 3.” The ten were the
TITMOUSE
boats, which had not appeared as separate units in the previous estimate. And the second area mentioned lay directly athwart SC 127’s new planned route: its center was 60 miles south of SC 127’s Point WM.