"One knot," Raeburn said.

"All back one third," Swanson said. No sharp imperatives, not ever, in the way Swanson gave his orders, more a quiet and conversational suggestion, but there was no mistaking the speed with which one of the crewmen strapped into the diving-stand bucket seat leaned forward to telegraph the order to the engine room. "Left full rudder."

Swanson bent over to check the plot, closely watching the tiny pinpoint of light and the tracing pencil move back toward the approximate center of the elongated triangle formed by the four red crosses. "All stop," he went on. "Rudder amidships." A pause, then: "All ahead one third. No. All stop."

"Speed zero," Raeburn said.

"Twenty-one twenty feet," Swanson said to the diving officer. "But gently, gently."

A strong, steady hum echoed in the control center. I asked Hansen, "Blowing ballast?"

He shook his head. "Just pumping the stuff out. Gives a far more precise control of rising speed and makes it easier to keep the sub on an even keel. Bringing a stopped sub up on a dead even keel is no trick for beginners. Conventional subs never try this sort of thing."

The pumps stopped. There came the sound of water flooding back into the tanks as the diving officer slowed up at the rate of ascent. The sound faded.

"Secure flooding," the diving officer said. "Steady on one hundred feet."

"Up periscope," Swanson said to the crewman by his side. An overhead lever was engaged, and we could hear the hiss of high-pressure oil as the hydraulic piston began to lift the starboard periscope off its seating. The gleaming cylinder rose slowly against the pressure of the water outside until finally the foot of the periscope cleared its well. Swanson opened the hinged hand grips and peered through the eye-piece.

"What does he expect to see in the middle of the night at this depth?" I asked Hansen.

"Never can tell. It's rarely completely dark, as you know. Maybe a moon, maybe only stars, but even starlight will show as a faint glow through the ice-if the ice is thin enough."

"What's the thickness of the ice above, in this rectangle?"

"The sixty-four-dollar question," Hansen admitted, "and the answer is that we don't know. To keep that ice machine to a reasonable size, the graph scale has to be very small. Anything between four and forty inches. Four inches we go through like the icing on a wedding cake: forty inches and we get a very sore head indeed." He nodded across to Swanson. "Doesn't look so good. That grip he's twisting is to tilt the periscope lens upward and that button is for focusing. Means he's having trouble in finding anything."

Swanson straightened. "Black as the earl of hell's waistcoat," he said conversationally. "Switch on hull and sail floodlights."

He stooped and looked again. For a few seconds only. "Pea soup. Thick and yellow and strong. Can't see a thing. Let's have the camera, shall we?"

I looked at Hansen, who nodded to a white screen that had just been unshuttered on the opposite bulkhead. "All mod cons, Doc, Closed-circuit TV. Camera is deck mounted under toughened glass and can be remote-controlled to look up or around."

"You could do with a new camera, couldn't you?" The TV screen was gray, fuzzy, featureless.

"Best that money can buy," Hansen said. "It's the water. Under certain conditions of temperature and salinity, it becomes almost completely opaque when flood-lit. Like driving into a heavy fog with your headlights full on."

"Floodlights off," Swanson said. The screen became quite blank. "Floodlights on." The same drifting, misty gray as before. Swanson sighed and turned to Hansen. "Well, John?"

"If I were paid for imagining things," Hansen said carefully, "I could imagine I see the top of the sail in that left corner. Pretty murky out there, Captain. Blindman's buff, is that it?"

"Russian roulette, I prefer to call it." Swanson had the clear, unworried face of a man contemplating a Sunday afternoon in a deck chair. "Are we holding position?"

"I don't know." Raeburn looked up from the plot. "It's difficult to be sure."

"Sanders?" This to the man at the ice machine.

"Thin ice, sir. Still thin ice."

"Keep calling. Down periscope." He folded the handles up and turned to the diving officer. "Take her up like we were carrying a crate of eggs atop the sail and didn't want to crack even one of them."

The pumps started again. I looked around the control room. Swanson excepted, everyone was quiet and still and keyed-up. Raeburn's face was beaded with sweat, and Sanders' voice was too calm and impersonal by half as he kept repeating, "Thin ice, thin ice" in a low monotone. You could reach out and touch the tension in the air. I said quietly to Hansen, "Nobody seems very happy. There's still a hundred feet to go."

"There's forty feet," Hansen said shortly. "Readings are taken from keel level, and there's sixty feet between the keel and the top of the sail. Forty feet minus the thickness of the ice-and maybe a razor-sharp or needle-pointed stalactite sticking down ready to skewer the «Dolphin» through the middle. You know what that means?"

"That it's time I started getting worried too?"

Hansen smiled, but he wasn't feeling like smiling. Neither Was I, not any more.

"Ninety feet," the diving officer said.

"Thin ice, thin ice," Sanders intoned.

"Switch off the deck flood, leave the sail flood on," Swanson said. "And keep that camera moving. Sonar?"

"All clear," the sonar operator reported. "All clear all around." A pause then: "No, hold it, hold it! Contact dead astern!"

"How close?" Swanson asked quickly.

"Too close to say. Very close."

"She's jumping!" the diving officer called out sharply. "Eighty, seventy-five." The «Dolphin» had hit a layer of colder water or extra salinity.

"Heavy ice, heavy ice!" Sanders called out urgently.

"Flood emergency!" Swanson ordered — and this time it was an order.

I felt the sudden build-up of air pressure as the diving officer vented the negative tank and tons of seawater poured into the emergency diving tank. But it was too late. With a shuddering, jarring smash that sent us staggenng, the «Dolphin» crashed violently into the ice above, glass tinkled, lights went out and the submarine started falling like a stone.

"Blow negative to the mark!" the diving officer called. High-pressure air came boiling into the negative tank; at our rate of falling, we would have been flattened by the sea pressure before the pumps could even have begun to cope with the huge extra ballast load we had taken aboard in seconds. Two hundred feet, two hundred and fifty, and we were still falling. Nobody spoke; everybody just stood or sat in a frozen position staring at the diving stand. It required no gift for telepathy to know the thought in every mind. It was obvious that the «Dolphin» had been struck aft by some underwater pressure ridge at the same instant as the sail had hit the heavy ice above. If the «Dolphin» had been holed aft, this descent wasn't going to stop until the pressure of a million tons of water crushed and flattened the hull and in a ificker of time snuffed out the life of every man inside it.

"Three hundred feet," the diving officer called out. "Three fifty — and she's slowing. She's slowing."

The «Dolphin» was still falling, sluggishly passing the four hundred-foot mark, when Rawlings appeared in the control room, tool kit in one hand, a crate of assorted lamps in the other.

"It's unnatural," he said. He appeared to be addressing the shattered lamp above the plot which he had immediately begun to repair. "Contrary to the laws of nature, I've always maintained. Mankind was never meant to probe beneath the depths of the ocean. Mark my words, these newfangled inventions will come to a bad end."

"So will you if don't keep quiet," Commander Swanson said acidly. But there was no reprimand in his face; he appreciated as well as any of us the therapeutic breath of fresh air that Rawlings had brought into that tension-laden atmosphere. "Holding?" he said to the diving officer.