‘Thank you, Captain,’ said Gus.

‘A word of warning, first, sir. It’s an informal group. This kind of work is often done by eccentric people, and correct naval uniform is not always worn. The officer in charge, Commander Rochefort, wears a red velvet jacket.’ Vandermeier gave a man-to-man grin. ‘You may think he looks like a goddamn homo.’

Chuck tried not to wince.

Vandermeier said: ‘I won’t say any more until we’re in the secure zone.’

‘Very good,’ said Gus.

They went down the stairs and into the basement, passing through two locked doors on the way.

Station HYPO was a windowless neon-lit cellar housing thirty men. As well as the usual desks and chairs, it had oversized chart desks, racks of exotic IBM machine printers, sorters and collators, and two cots where the cryptanalysts took naps during their marathon codebreaking sessions. Some of the men wore neat uniforms but others, as Vandermeier had warned, were in scruffy civilian clothing, unshaven, and – to judge by the smell – unwashed.

‘Like all navies, the Japanese have many different codes, using the simplest for less secret signals, such as weather reports, and saving the complex ones for the most highly sensitive messages,’ Vandermeier said. ‘For example, call signs identifying the sender of a message and its destination are in a primitive cipher, even when the text itself is in a high-grade cipher. They recently changed the code for call signs, but we cracked the new one in a few days.’

‘Very impressive,’ said Gus.

‘We can also figure out where the signal originated, by triangulation. Given locations and the call signs, we can build up a pretty good picture of where most of the ships of the Japanese navy are, even if we can’t read the messages.’

‘So we know where they are, and what direction they’re taking, but not what their orders are,’ said Gus.

‘Frequently, yes.’

‘But if they wanted to hide from us, all they would have to do is impose radio silence.’

‘True,’ said Vandermeier. ‘If they go quiet, this whole operation becomes useless, and we are well and truly fucked up the ass.’

A man in a smoking jacket and carpet slippers approached, and Vandermeier introduced the head of the unit. ‘Commander Rochefort is fluent in Japanese, as well as being a master cryptanalyst,’ Vandermeier said.

‘We were making good progress decrypting the main Japanese cipher until a few days ago,’ Rochefort said. ‘Then the bastards changed it and undid all our work.’

Gus said: ‘Captain Vandermeier was telling me you can learn a lot without actually reading the messages.’

‘Yes.’ Rochefort pointed to a wall chart. ‘Right now, most of the Japanese fleet has left home waters and is heading south.’

‘Ominous.’

‘It sure is. But tell me, Senator, what’s your reading of Japanese intentions?’

‘I believe they will declare war on the United States. Our oil embargo is really hurting them. The British and the Dutch are refusing to supply them, and right now they’re trying to ship it from South America. They can’t survive like this indefinitely.’