'It's not coming right at us. It should pass us about eleven hundred metres off the port bow.' The duty officer repeated the message to the captain. They listened, ummoving, as the sound peaked and then diminished slightly with a perceptible change in pitch. Washington noted its passage through the ship's depth level, headed for the surface.

Abruptly the noise ceased, to be replaced with an almost painful silence as saturated ears tried to adjust. Active dials lapsed into quiescence and the bright blip on the screen disappeared. Washington swivelled in his chair to exchange wide-eyed looks of surprise with the duty officer who reported once more to the captain.

Washington returned his attention to his instruments. Ten, fifteen seconds went by. Slowly he turned up the sensitivity of the device and the volume on the speaker and earphones. Only the routine sounds of the sea issued. After twenty-five seconds the duty officer still stood with the phone clamped in a sweaty hand, but others in the cabin began to shuffle in relief. Washington increased the gain a bit more and concentrated his trained ear to detect any hint of abnormal sound. He systematically switched display modes but found no clue to the thing that had just assaulted them.

With the suddenness and impact of a physical blow, the cabin filled with the sound again. Washington shrieked, ripped off his earphones and slapped a palm over each ear. He slipped off his chair and knelt in a daze of confusion, his body pumped with adrenalin, his ears ringing with an intense hollow echo. Several figures rushed to the sonar console. Two friends bent to Washington. Someone fumbled, then found, the volume control. The frightening hiss dropped to a muted roar and the duty officer was left in the new quiet, shouting hoarsely into the phone.

The noise dropped gradually, and then just before it faded below a perceptible level it ceased abruptly once more. Silence fell in the cabin, broken only by the chatter of the sonar and the quiet moan of the man who remained on the floor, rocking gently, his hands over his ears and his eyes squeezed shut.

Several days after the cancellation of Project QUAKER, Isaacs played a closely fought game of handball with a friend and colleague. Captain Avery Rutherford, one of the senior officers in Naval Intelligence. Rutherford was three years older than Isaacs, but in excellent shape. They split the first four games and went to a tie breaker on the match game. Isaacs scored once and served at game point. After several volleys, Isaacs took a shot in front court. Calculating to catch his opponent off guard, he hit the ball softly to the front wall, but it went a bit too high and gave Rutherford time to cover it. With Isaacs in the front court, Rutherford played a favourite shot which came off the front wall as a lob calculated to land in the rear corner, a troublesome left hand return at best. He then retreated rapidly to centre court just behind the service area to await the return, hoping to hear the satisfying silence of a missed shot.

Isaacs knew the other man's tactics, however, and back— pedalled furiously to cover most of the distance to the left rear corner before the ball left the front wall. This gave him time to plant his feet firmly, eye locked on the descending sphere. The ball bounced on the floor, then off the back wall, nicely clearing both it and the side wall. Isaacs made the shot at hip level, putting into it everything his weaker left hand could muster. The ball rifled cross court, just missing Rutherford 's left knee. It struck almost dead in the corner, the from wall a fraction of a second earlier than the right, two inches above the floor. It skittered once and then meekly rolled across the court to bump gently into Rutherford 's toe.

The sudden denouement caught Rutherford by surprise and he just stared at the ball. Then he scooped it up and turned.

'Damnation, Bob, that was a hell of a shot!'

'Thanks,' Isaacs grinned. 'Amazingly enough, that's just what I wanted it to do.'

They played two more games for exercise, but without quite the fire. Isaacs took the first by a comfortable margin, Rutherford the last.

After the game, they left sweat-sagged piles of gym clothes in front of their lockers, grabbed their towels and stepped into the steam room. They sat on the bench and rehashed their play, each enthusiastically recalling the other's good points and mixing in an occasional soft-pedalled critique.

They fell silent for a couple of minutes. Then Rutherford swivelled his head and looked at his companion.

'Do you mind a little shop talk, off the cuff?'

Isaacs leaned back against the wall, his eyes closed.

'Of course not, what's on your mind?'

'Well, we've had scattered reports of a strange acoustic phenomenon, sort of an underwater sonic boom. This thing's been kicking around. Nobody's done anything about it because no one knows what to make of it. I just wondered whether it might ring a bell with you?'

'No,' said Isaacs lethargically, 'I haven't heard anything about it. We've been up to our ears counting screws and bolts in Tyuratam, waiting for them to launch the other shoe. Some kind of explosion?'

'No,' Rutherford shook his head and pinched some sweat out of his eyes, 'it's not localized like that. Something seems to be moving through the water, making a hell of a racket as it goes. It comes from the ocean bottom and apparently disappears momentarily at the surface. Then, it reappears and proceeds back down to the bottom.'

'Some kind of missile, torpedo?'

'Seems like it, doesn't it? But there's no indication of any launching craft. Besides this starts from really deep down, miles.'

'How about an underwater volcano, maybe spewing out blobs of lava, or rocks?'

'There's probably too much drag in the water for that to be possible, but I'd give some credence if the reports were from one spot. They're not, though. They're from all over the globe. Several from mid-Atlantic shipping lanes, a few near Japan, a couple from the Sixth Fleet in the Med, one south of Madagascar, another in the Sea of Tasman between Australia and New Zealand. The latest one came from a sub north of Hawaii , that's why it's on my mind. A particularly close call, poor bastards thought they were being attacked. Anyway, the thing seems 'to hop all over.'

The men fell silent. Rutherford leaned over to examine a chipped nail on his big toe. Isaacs had not really been concentrating on the conversation. Now snippets of it rolled around in his head. Suddenly, a surge of adrenalin went keening out of his belly and through his body. His eyes snapped open and, despite the heat, he felt as if someone had just raked a large icy comb down his back.

He sat up and faced Rutherford who still bent over his foot.

'Those reports you just described, they seem to be either north or south of the equator, about equal distances.' He tried to keep his voice casual.

'Oh yeah, I forgot to mention another curious feature. This thing appears at random times, not always near the same latitude, sometimes north, sometimes south.'

'Thirty-three degrees.'

Now Rutherford swivelled his head in surprise.

'Hey, friend, you've been holding out on me!'

Nervous energy drove Isaacs off the bench. 'Nothing like it,' he said intently, 'just slow to make the connection.' He paced the small room randomly, oblivious to his steamy surroundings, his mind racing. 'Good lord, in the water, too! What the hell does that mean?'

Rutherford had witnessed his friend's burst of intensity before and, failing to understand what had set him off, watched bemusedly as Isaacs moved about, his cock flipping drops of sweat and condensed steam at each sudden turn.

Isaacs stopped in front of him.

'Up to last week we were analysing the seismic equivalent of your phenomenon. Something's moving through the earth, generating seismic waves.'