"We don't know," Illya said. "Our whole scheme is predicated on the assumption that they don't. Having taken all this trouble to build a secret place where nobody can observe them, making their own sea to sail on as it were, we imagine they'll feel secure enough not to have bothered. No scheduled air corridors cross the region and we can see no reason for them to have guarded against air or water invasion - in the first place, there's nothing for a plane to see; and in the second, how can there be any other craft on the lake when it's just been made and their underwater base is the only dock on it?... All the same, to be honest, we don't actually know. And if they can tape planes, they'll be on to us!"
"We'd better keep our fingers crossed for each other, then, hadn't we?" the navy man said agreeably. "Now come on - in you go."
The girl bunched her hair on top of her head and dragged on the tight-fitting rubber helmet. Highlights slid along the surface of the polished latex as she reached up to set the oval mask in place. A moment later she was lowering herself into the tiny rear compartment of the submarine.
Illya climbed into the forward cockpit, turned to give her the thumbs-up sign, and lowered the perspex nacelle over his head and shoulders. The navy man screwed down both the transparent hatches and shortly after wards they felt the helicopter sinking towards the lake invisible in the darkness below them. The cigar-shaped craft with its twin blisters, despite its aerodynamic shape, lurched sickeningly and swayed from side to side on its guide ropes when the bomb bay doors were opened and the helicopter crew winched them slowly down towards the water. Through the perspex, they could see the drowned valley curving away to the southwest, fifteen or twenty miles of smooth lead foil among the darkness of the jagged hills. Lights pricked the dark to the south and northeast, but they were a long way away. Immediately below, there was not a sign of life.
They hit the water stern first with a ringing slap that echoed thunderously in the tiny craft. Half a minute later, they were pitching uneasily in the choppy waves agitating the surface of the lake. The helicopter, having activated the automatic release grapples on the guides, rose into the night and clattered away towards Brasilia
Kuryakin immediately switched on the motors and took the sub beneath the surface. Coralie Simone had a fleeting impression of waves splashing towards her up the inclined surface of the screen that was so close to her eyes, and then they were in a blackness so intense that it almost hurt. She was aware of a complex hum from the electric propulsion system and its auxiliaries - and of a dark and heavy chill that pervaded the air in the minute cockpit and numbed her senses.
"We shall have to hurry," Kuryakin's amplified voice split the silence from the intercom by her ear. "The air's very limited and we don't dare use the cylinders in case we have to get out underwater. Can you get the equipment working right away?"
"Of course," the girl said, and she willed her hands to the tasks they had learned that afternoon. There were two systems aboard: the usual echo-sounding device for revealing subterranean topography, other shapes in the sea and so on, and a more modern technique, analogous to the system used in air-to-air missiles, homing on the heat energy released by the motors of the quarry.
"Do you think they'll have the same equipment on their submarine?" she asked as she busied herself with dials and indicators.
"I would guess not," Illya said. "We hope not, anyway. Even if they have it, they'd hardly have it in use. I mean, they'd use the navigational aids, of course - but why would they watch a screen for possible enemy ships when it's their lake and they know they're the only ships, in it?"
"I suppose you're right. But if they did have it... and use it?'
"Then we'd be lost," the agent said shortly. "Are you getting anything interesting yet?"
"It's a bit difficult at first - especially since I'm not really a trained operator. And there are still so many objects on the valley floor - houses, I suppose, and trees and walls and so on - that it's really impossible to sort out... Wait a minute! Here's something... It's something big, very big!"
She began reading off figures and Kuryakin concentrated on his dials and controls. "It will be the nuclear submarine, will it, if it proves to be moving?" she asked.
"Bound to be. According to Napoleon, they only test at night - to avoid any possible witnesses, no doubt. What do you see?"
"It is moving. - And my goodness, Illya, it must be enormous!"
Kuryakin switched on his monitors. "Yes, you're right," he said, "It is pretty generously built. Seems to be on a cross-course some way above us."
"How deep are we?" the girl asked.
"About ten fathoms. From the disturbance, I should judge that the sub's actually on the surface - or at the most only half submerged. We'll go on up and see bow near we can get."
Now gaining, now falling behind, the midget sub marine stalked the nuclear vessel in the black waters of the lake. The skipper of the Thrush craft was adopting an erratic course, zigzagging from side to side of the reservoir, accelerating and slowing every few minutes.
"He's testing the surface maneuverability," Illya said. "Must be. I only wish we could surface too. It would be so much easier to keep track of him. But we don't dare - there might be a phosphorescent wake, a too-smart look out, anything. Well just have to hope he goes in soon."
Once, concentrating too closely on the livid radiance of the radar screens, they almost rammed the tiny craft straight into a massive wall of rock that rose straight from the valley floor. Another time, the nuclear sub marine took them by surprise making a tight U-turn and passing almost directly overhead in the opposite direction.
Looking up through their perspex domes at the faint hint of light drifting down from the surface, they watched the great hull - only inches above their eyes, it seemed - draw smoothly past. A shark shape, sinister and efficient, blotting out the light.
Shortly afterwards, there was a commotion in the water around them and the midget rocked violently. The big submarine was submerging.
"It crash-dived fifty fathoms," Illya exclaimed - it had taken them some time to locate it again on their screens - "and now it's scooting along the floor of the old valley for all it's worth!"
They followed the nuclear craft up to the far end of the dam and then back to the barrage again, where they "froze" near the rock face to minimize the risk of detection as the bigger vessel turned. "And off she goes again," Kuryakin said in exasperation. "But the power of that thing! Do you realize the speed she's doing on those straight runs? Why, on that last one, she was hitting -"
"Illya!" Coralie's voice was urgent over the intercom. "Be quiet a moment, will you? She's altered course through ninety degrees; she's turned off to port, towards the side of the dam. I think she may be going in."
"Okay. I'll try to catch up and tail her. At the last stage, I'll have to follow her by eye - for the only thing we can do is to follow her into this pen if possible - and hope that nobody spots us before they pump out the water!"