In 1969, USS Chopper (SS-342), a WWII-era fleet submarine that had been converted to Cold War configurations, executed a maneuver that no submarine could be expected to survive. There were no fatalities, but there were several serious injuries. It is difficult to explain.

No one thing went seriously wrong. But one minor mechanical malfunction, followed by a series of human errors and heroic efforts, plus an additional mechanical malfunction that no one anticipated, created a situation that is still discussed in textbooks, and in submarine wardrooms, today.

Chopper was cruising at a reasonably shallow depth off the south coast of Cuba when there was a loss of AC power. Since AC power was largely considered a luxury, and not a necessity, there were simple DC-powered backup systems for the normal AC systems involved in the submarine's control and indication systems.

However the bow planesman, the first person to notice the loss of AC power, did not say, "Loss of normal indication," which he should have said. He said, "Loss of normal." The diving officer did not understand, and assumed that the planesman was reporting loss of normal power to the planes. So the diving officer responded by giving the order to shift the bow and stern planes to hand operation.

The diving planes can be operated by hand, but they respond very slowly, and the planesmen get tired very quickly, since they are substituting muscle power for the normal hydraulic power at 600 psi of working pressure.

What had happened was that the planesmen were looking at the normal plane position indicators to control the planes, and by the time they discovered the problem they had inadvertently deflected both planes to the full dive position. By the time they discovered their mistakes, they had been ordered to use hand power to correct the problem. It took much too long.

Since Chopper was on a training exercise, she happened to be moving unusually fast through the water, so the mistake with the planes caused the boat to achieve a down angle of 86 degrees from horizontal. This is not good. Any angle of greater than 25 degrees has to be reported to ComSubLant along with a report of appropriate "corrective" measures.

As the down angle exceeded 20 degrees, the second mechanical malfunction kicked in. There was a loose metal plate in the junction box that housed all of the interior communications circuits. This metal plate fell over in such a way as to short out every communication circuit on the submarine.

The officer of the deck realized the problem with the controls, and ordered the main motors to switch from ahead full to back full. However, this order could not be transmitted to the maneuvering room, because the normal AC-powered systems were inoperative, and the DC-powered and sound-powered systems were shorted out.

As Chopper achieved an unprecedented down angle, the senior controllerman in the maneuvering room tried to communicate with the conning tower to ask what was going on. He quickly figured out that he had no communications. He looked at a sea pressure gauge at his elbow, and realized that they were passing through test depth. So he unilaterally made the decision to switch the main propulsion motors from full ahead to full astern. He saved everyone's life with that action.

Chopper stopped descending with the bow at approximately two-and-a-half times test depth. The proof of this was that the sea pressure gauge in the forward escape trunk had broken its needle against the pin at the end of the gauge. The 86-degree down angle was reconstructed by observing that the clock had fallen off the bulkhead in the wardroom. Investigators later cut that section off the bulkhead and experimented, and determined that it required an 86-degree angle to cause the clock to fall.

Meanwhile, the diving officer, who was unable to communicate with the maneuvering room, had given the order to use the high pressure air to blow the main ballast tanks. When the submarine stopped descending, and began to rise as the result of the reversed main motors and the ballast blow, the boat rotated vertically about the stern, and the bow proceeded to surface.

Chopper's bow did indeed surface. The entire forward end of the submarine broke the surface, including part of the sail, or conning tower. This was visually observed by the crew of USS Hawkins (DD-873), the destroyer that was conducting the exercise against Chopper.

Investigators later determined, by measuring the amount of fat that remained in the deep fat fryer, that Chopper's up angle was 87 degrees when she broke the surface.

Chopper then sank back into the water on an even keel. Everyone breathed a sigh of relief. However, now there was no electrical power on board at all, since the battery breakers had tripped when the steep angles were experienced. Later generations of circuit breakers were designed not to fail under simple tilting maneuvers. But Chopper was without power. She was also without compressed air, since they had used up the entire supply in the initial panic. After a few moments of sitting normally, the crew noticed that they were descending again, and there seemed to be nothing that they could do. The diving officer felt that they had survived to crisis, only to die in the aftermath.

The submarine slowly descended to a keel depth of 240 feet, paused, and then even more slowly ascended to the surface. The electricians crawled down in the battery wells, slithered across the spilled battery acid on their stomachs, and re-set the battery circuit breakers. The hydraulics kicked in, so the officer of the deck could raise the periscope and verify that they were near the surface. The snorkel mast was raised. The machinist's mate started the low pressure blower to empty the main ballast tanks. Chopper finally surfaced, for the last time.

Later that year, when I was in Submarine School, the instructors seemed to be particularly eager to teach us about this incident.