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In January, 1969, USS Chopper, a WWII-era fleet submarine that had been converted to post-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 could have 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 on those old boats, 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 normal 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 trying to use the normal plane position indicators, and 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.

The submarine was engaged in a training exercise, and 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 disciplinary 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 sound-powered interior communications circuits. This metal plate fell over in such a way as to short out every such communication circuit on the boat.

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 the submarine 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 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.

The submarine 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 consistently 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.

The bow of the Chopper did indeed surface. The entire forward end of the submarine broke the surface vertically, including part of the sail, or conning tower. This was visually observed by the crew of the destroyer that was conducting an exercise against the Chopper.

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

The submarine 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 the Chopper was without power. It 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 officer of the deck raised the periscope and verified that they were near 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 snorkel mast could be raised. The machinist's mate then started the low pressure blower to empty the main ballast tanks, and the Chopper finally surfaced, for the last time.

Five months later, when I arrived at Submarine School, the instructors seemed to be eager to teach us about this incident.

The sailors who survived the Chopper incident were known around the submarine force as DDMFs, or deep-diving mother fuckers. They couldn't buy drinks at the base clubs after that.

One sailor from the Chopper had been a mess cook at the time of the incident. He was one of the ones who remained in the submarine force, and he was transferred to the Odax, my boat. One night when I was diving officer, that sailor was the helmsman. We began a routine descent from periscope depth, and we lost AC power at that moment. We recovered quickly and competently, achieving a ten-degree down angle instead of the five degrees that I had ordered. Since we shot below the ordered keel depth of 100 feet, I ordered a ten-degree up angle to stop our descent and to return to ordered depth. Everything worked fine. Except, the helmsman froze. The Officer of the Deck and the Quartermaster had to physically overpower the helmsman to get his hands off the motor order telegraph handles. We relieved him of duty, and we sent him off to a surface ship the minute we arrived in port.

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