"A hundred miles, as Dr. Carpenter said," Raeburn confirmed after a short calculation. "At least that."

"So. We leave here and take a course oh forty. Not enough to take us very far from their general direction, but it will give us enough off-set to take a good cross-bearing eventually. We will go exactly a hundred miles and try for another polynya. Call the executive officer, secure for diving." He smiled at me. "With two cross-bearings and an accurately measured base line, we can pin them down to a hundred yards."

"How do you intend to measure a hundred miles under the ice? Accurately, I mean?"

"Our inertial-navigation computer does it for me. It's very accurate: you wouldn't believe just how accurate. I can dive the «Dolphin» off the eastern coast of the United States and surface again in the eastern Mediterranean within five hundred yards of where I expect to be. Over a hundred miles I don't expect to be twenty yards out."

Radio aerials were lowered, hatches screwed down, and within five minutes the «Dolphin» had dropped down from her hole in the ice and was on her way. The two helmsmen at the diving stand sat idly smoking, doing nothing: the steering controls were in automatic interlock with the inertial-navigation system, which steered the ship with a degree of accuracy and sensitivity impossible to human hands. For the first time I could feel a heavy jarring vibration rumbling throughout the length of the ship. "Can't last many hours," the message had said. The «Dolphin» was under full power.

I didn't leave the control room that morning. I spent most of the time peering over the shoulder of Dr. Benson, who had passed his usual five minutes in the sick bay waiting for the patients who never turned up and then had hurried to his seat by the ice machine. The readings on that machine meant living or dying to the Zebra survivors. We had to find another polynya to surface in to get a cross-bearing on Zebra's position: no polynya, no cross-bearing; no cross-bearing, no hope. I wondered for the hundredth time how many of the survivors of the fire were still alive. From the quiet desperation of the few garbled messages that Brown and Zabrinski had managed to pick up, I couldn't see that there would be many.

The pattern traced out by the hissing stylus on the chart was hardly an encouraging sight. Most of the time it showed the ice overhead to be of a thickness of ten feet or more. Several times the stylus dipped to show thicknesses of thirty to forty feet, and once it dipped down almost clear of the paper, showing a tremendous inverted ridge of at least 150 feet in depth. I tried to imagine what kind of fantastic pressures created by piled-up log jams of rafted ice on the surface must have been necessary to force ice down to such a depth; but I just didn't have the imagination to cope with that sort of thing.

Only twice in the first eighty miles did the stylus trace out the thin black line that meant thin ice overhead. The first of those polynyas might have accommodated a small row boat, but it would certainly never have looked at the «Dolphin»; the other had hardly been any bigger.

Shortly before noon the hull vibration died away as Swanson gave the order for a cut-back to a slow cruising speed. He said to Benson, "How does it look?"

"Terrible. Heavy ice all the way."

"Well, we can't expect a polynya to fall into our laps right away," Swanson said reasonably. "We're almost there. We'll make a grid search. Five miles east, five miles west, a quarter mile farther to the north each time."

The search began. An hour passed, two, then three. Raeburn and his assistant hardly ever raised their heads from the plotting table, where they were meticulously tracing every movement the «Dolphin» was making in her criss-cross search under the sea. Four o'clock in the afternoon. The normal background buzz of conversation, the occasional small talk from various groups in the control center, died away completely. Benson's occasional "Heavy ice, still heavy ice," growing steadily quieter and more dispirited, served only to emphasize and deepen the heavy, brooding silence that had fallen. Only a case-hardened undertaker could have felt perfectly at home in that atmosphere. At the moment, undertakers were the last people I wanted to think about.

Five o'clock in the afternoon. People weren't looking at each other any more, much less talking. Heavy ice, still heavy ice. Defeat, despair hung heavy in the air. Heavy ice, still heavy ice. Even Swanson had stopped smiling. I wondered if he had in his mind's eye what I now constantly had in mine: the picture of a haggard, emaciated, bearded man with his face all but destroyed with frostbite, a frozen, starving, dying man draining away the last few ounces of his exhausted strength as he cranked the handle of his generator and tapped out his call sign with lifeless fingers, his head bowed as he strained to listen above the howl of the ice storm for the promise of aid that never came. Or maybe there was no one tapping out a call sign any more. They were no ordinary men who had been sent to man Drift Ice Station Zebra, but there comes a time when even the toughest, the -bravest, the most enduring will abandon all hope and lie down to die. Perhaps he had already lain down to die. Heavy ice, still heavy ice.

At half-past five Commander Swanson walked across to the ice machine and peered over Benson's shoulder. He said, "What's the average thickness of that stuff above?"

"Twelve to fifteen feet," Benson said. His voice was low and tired. "Nearer fifteen, I would say."

Swanson picked up a phone. "Lieutenant Mills? Captain here. What is the state of readiness of those torpedoes you're working on? Four? Ready to go? Good. Stand by to load. I'm giving this search another thirty minutes, then it's up to you. Yes, that is correct. We shall attempt to blow a hole through the ice." He replaced the phone.

Hansen said thoughtfully, "Fifteen feet of ice is a helluva lot of ice. And that ice will have a tamping effect and will direct ninety per cent of the explosive force down the way, You think we «can» blow a hole through fifteen feet of ice, Captain?"

"I've no idea," Swanson admitted. "How can anyone know until we try it?"

"Nobody ever tried to do this before?" I asked.

"No. Not in the U.S. Navy, anyway. The Russians may have tried it, I wouldn't know. They don't," he added dryly, "keep us very well informed on those matters."

"Aren't the underwater shock waves liable to damage the «Dolphin?»" I asked. I didn't care for the idea at all, and that was a fact.

"If they do, the Electric Boat Company can expect a pretty strong letter of complaint. We shall explode the warhead electronically about a thousand yards after it leaves the ship: it has to travel eight hundred yards anyway before a safety, device unlocks and permits the warhead to be armed. We shall be bows on to the detonation, and with a hull designed to withstand the pressures this one is, the shock effects should be negligible."

"Very heavy ice," Benson intoned. "Thirty feet, forty feet, fifty feet. Very, very heavy ice."

"Just too bad if your torpedo ended up under a pile like the stuff above us just now," I said. "I doubt if it would even chip off the bottom layer."

"We'll take care that doesn't happen. We'll just find a suitably large layer of ice of normal thickness, kind of back off a thousand yards, and then let go."

"Thin ice!" Benson's voice wasn't a shout, it was a bellow. "Thin ice. No, by God, clear water! Clear water! Lovely, clear, clear water!"

My immediate reaction was that either the ice machine or Benson's brain had blown a fuse. But the officer at the diving panel had no such doubts, for I had to grab and hang on hard as the «Dolphin» heeled over violently to port and came curving around, engines slowing, in a tight circle to bring her back to the spot where Benson had called out. Swanson watched the plot, spoke quietly, and the big bronze propellers reversed and bit into the water to bring the «Dolphin» to a stop.