Winter of the World

They always started with small things. The last word of any signal was often OWARI, meaning end. The cryptanalyst would look for other appearances of that number group in the same signal, and write ‘END?’ above any he found.

The Japanese helped them by making an uncharacteristically careless mistake.

Delivery of the new code books for JN-25b was delayed to some far-flung units. So, for a fatal few weeks, the Japanese high command sent out some messages in both codes. Since the Americans had broken much of the original JN-25, they were able to translate the message in the old code, set the decrypt alongside the message in the new code, and figure out the meanings of the five-digit groups of the new code. For a while they progressed by leaps and bounds.

The original eight cryptanalysts were supplemented, after Pearl Harbor, by some of the musicians from the band of the sunk battleship California. For reasons no one understood, musicians were good at decoding.

Every signal was kept and every decrypt filed. Comparison of one with another was crucial to the work. An analyst might ask for all the signals from a particular day, or all the signals to one ship, or all the signals that mentioned Hawaii. Chuck and the other clerical staff developed ever-more-complex systems of cross-indexing to help them find whatever the analysts needed.

The unit predicted that in the first week of May the Japanese would attack Port Moresby, the Allied base in Papua. They were right, and the US Navy intercepted the invasion fleet in the Coral Sea. Both sides claimed victory, but the Japanese did not take Port Moresby. And Admiral Nimitz, Commander-in-Chief of the Pacific, began to trust his codebreakers.

The Japanese did not use regular names for locations in the Pacific Ocean. Every important place had a designation consisting of two letters – in fact, two characters or kanas of the Japanese alphabet, although the codebreakers usually used equivalents from the Roman A to Z. The men in the basement struggled to figure out the meaning of each of these two-kana designators. They made slow progress: MO was Port Moresby, AH was Oahu, but many were unknown.

In May, evidence was fast building up of a major Japanese assault at a location they called AF.

The best guess of the unit was that AF meant Midway, the atoll at the western end of the fifteen-hundred-mile-long chain of islands that started at Hawaii. Midway was halfway between Los Angeles and Tokyo.

A guess was not enough, of course. Given the numerical superiority of the Japanese navy, Admiral Nimitz had to know.

Day by day, the men Chuck was working with built up an ominous picture of the Japanese order of battle. New planes were delivered to aircraft carriers. An ‘occupation force’ was embarked: the Japanese were planning to hold on to whatever territory they won.

It looked as if this was the big one. But where would the attack come?

The men in the basement were particularly proud of decoding a signal from the Japanese fleet urging Tokyo: ‘Expedite delivery of fuelling hose.’ They were pleased partly because of the specialized language but mainly because the signal proved that a long-range mid-ocean manoeuvre was imminent.

But the American high command thought the attack might come at Hawaii, and the army feared an invasion of the west coast of the United States. Even the team at Pearl Harbor had a nagging suspicion it could be Johnston Island, an airstrip a thousand miles south of Midway.

They had to be one hundred per cent certain.

Chuck had a notion how it might be done, but he hesitated to say anything. The cryptanalysts were so clever, and he was not. He had never done well in school. In third grade a classmate had called him Chucky the Chump. He had cried, and that had guaranteed that the nickname would stick. He still thought of himself as Chucky the Chump.

At lunchtime he and Eddie got sandwiches and coffee from the commissary and sat on the dockside, looking across the harbour. It was returning to normal. Most of the oil had gone, and some of the wrecks had been raised.

While they were eating, a wounded aircraft carrier appeared around Hospital Point and steamed slowly into harbour, trailing an oil slick that stretched all the way out to sea. Chuck identified the vessel as the Yorktown. Her hull was blackened with soot and she had a huge hole in the flight deck, presumably caused by a Japanese bomb in the Battle of the Coral Sea. Sirens and hooters sounded a congratulatory fanfare as she approached the Navy Yard, and tugs assembled to nudge her through the open gates of No. 1 Dry Dock.

‘She needs three months’ work, I hear,’ Eddie said. He was based in the same building as Chuck, but in the naval intelligence office upstairs, so he got to hear more gossip. ‘But she’s putting to sea again in three days.’

‘How are they going to manage that?’