Sinking and Escape from the B.A.P Pacocha (ex USS Atule SS 403)


Enclosure (1) to 491:MW-96-79558

The B.A.P. PACOCHA (SS-48) Collision: The Escape and Medical Recompression Treatment of Survivors Special Report SP89-1

By Captain C. Harvey, M.D., MC, USN And Commander J. Carson, M.D., MC, USN Naval Submarine Medical Research Laboratory Box 900, Naval Submarine Base New London Groton, CT 06349-5900

30 March 1989


At the invitation of the Peruvian Navy, a U.S. Navy Team review the circumstances surrounding the collision, sinking, and subsequent escape and rescue of members of the B.A.P. PACOCHA. Approximately half were rescued after immediate escape before the sinking with a 2-4 hour cold-water exposure, and the other half were trapped for over 20 hours in the forward torpedo room. They escaped by buoyant ascent, after having been subjected to pressure from partial flooding and air being introduced from the air banks. Escapees suffered decompression sickness and gas emboli after surfacing. The medical response, rescue, evacuation, and recompression treatment of survivors using all available equipment and personnel is reviewed. Some observations are presented that might diminish morbidity and mortality in the future.

The Problem

At the request of the Peruvian Navy, a United States Navy Assist Team, consisting of two experienced Undersea Medical Officers, reviewed the medical response, rescue, evacuation, and recompression treatment following the sinking of the B.A.P. PACOCHA on 26 August 1988.

The Findings

Approximately half were rescued after immediate escape before the sinking with a 2-4 hour cold-water exposure. The other half were trapped for over 20 hours in the forward torpedo room after sinking. Escapees suffered decompression sickness and gas emboli after surfacing. Procedures and treatments were revived.


Some observations are presented that might diminish morbidity and mortality in the future.


The research was carried out at the request of the Peruvian Navy and under Naval Medical Research and Development Command Work Unit 63713N M0099.01A-5012, “(U) Medical problems associated with pressurized submarine rescue.” This special report was approved for release on 30 March 1989 and designated NSMRL Special Report SP89-1.


A United States Navy Assist Team, consisting of two experienced Undersea Medical Officers, Visited the Peruvian Navy from 31 January thru 2 February 1989 to review the lessons learned from escape and rescue operations following the sinking of the B.A.P. PACOCHA on 26 August 1988. This report summarizes the information available, discusses implications, and makes recommendations for consideration by both countries.

The B.A.P. PACOCHA was transiting to its homeport on the surface, when it was struck on the aft, port quarter by the ice-breaking bow of the KIOWA MARU at 1850 on 26 August 1988. No Collision alarm was sounded and bulkheads were not sealed at the time of impact. PACOCHA sunk to a keel depth of 140 feet in 5 minutes and the KIOWA MARU continued on to port, unaware of what it had hit. Twenty-three people escaped into the water as the boat sank. Three of these died of exposure prior to the arrival of help two and 1.2 hours later. Three people died in flooded compartments and the Captain of the vessel died in the sail while closing the bridge access hatch. Twenty-two people survived in the PACOCHA, ultimately retreating to the forward torpedo room as the atmosphere in the boat became contaminated. Pressure in the submarine was elevated from the start and later was calculated to have reached 54 feet of sea water gauge pressure over the next 17 ½ hours. The United States Fly-away McCann rescue system was activated, but aborted in transit when deterioration of the atmosphere within the PACOCHA led to a decision to use buoyant escape techniques. The escape, completed by the twenty-three hour mark, resulted in twenty of the twenty-two escapees developing symptoms of decompression sickness. All were ultimately treated with recompression therapy. One died, one is severely brain injured, and several have residual injuries from decompression sickness. Implications for procedures training, support and equipment modifications are discussed in this report.


The following narration of events was complied from interviews conducted 31 January – 2 February 1989, with numerous parties, including Rear Admiral Guillermo Tirado, Commander of the Submarine Flotilla, five survivors who were trapped in the submarine, four divers involved in the escape, five physicians involved in the recompression treatments, and four physicians involved in subsequent hospital treatments. The members of the Assist Team from the United States were Captain C. A. Harvey, MC, USN, Commanding Officer, Naval Submarine Medical Research Laboratory and Commander J. F. Carson, Senior Medical Officer, Submarine Development Group One. Both are Undersea Medical Officers familiar with submarine escape and rescue techniques in the U. S. Navy.

Fluency in English was variable. Rear Admiral Tirado, a 1962 graduate of the U. S Naval Academy, was highly fluent and most cooperative. He spent an entire morning providing a candid narrative of events as recorded in his investigation. Two of the dives and one of the physicians involved in the recompression treatment were able to converse in English, and two of the hospital physicians were also conversant in English. All others possessed little or no English capabilities.

Since neither of the interviewers spoke Spanish, much of the information was narrated through an interpreter. We were most fortunate in this regard to have the services of a Peruvian Medical Officer, LT Guillermo “Willie” Alexander Smith, who was highly fluent in English. Although he was not trained in Diving or Submarine Medicine, which might have helped us gain better information more quickly, he was interested, , motivated, and did an outstanding job. We were most grateful for his services, without which we would not have been able to function or resolve conflicts in information. The combination of a language barrier, elapsed time since the accident and perhaps misinterpretation of statements may have produced errors in this report. If so, the team members apologize. Nevertheless there are valuable lessons and experiences to share with all who serve beneath the sea. It is in this spirit that this report is submitted.


Friday, 26 Aug 88

1820 - Sunset.

1850 - Collision.

Following torpedo exercise, the PACOCHA, (Former USS Atule SS-403, transferred to Peru in 1974), was transiting to the Port of Callao on the surface with a 1900 hr ETA. The forward torpedo room, and bridge hatches as well as the main induction valve were open. Forty-nine people were aboard, including the Squadron Commander to conduct an operational readiness inspection.

The KIOWA MARU, a 412-ton Japanese fishing trawler was sighted by lookouts and by the Officer of the Deck prior to the collision. It apparently was “lit up like a Christmas tree and those on board had difficulty determining its bearing. The personnel of the PACOCHA felt they had the right of way and waited for the KIOWA MARU to maneuver, which it didn’t. Last minute maneuvers by PACOCHA failed to avoid the collision, which occurred at 1850 hours when the bow of the KIOWA MARU struck the PACOCHA in the aft port quarter.

Damage was severe because the KIOWA MARU’s bow was reinforced for ice breaking and had a sub-surface protrusion for that purpose. The PACOCHA was opened like a tin can. The ballast tank and fuel oil tank in the area of impact were ruptured, and a 2 meter by 10 centimeter split in the pressure hull resulted along the weld seam where the pressure hull widens aft of the ballast tanks. Through this split, both fuel oil and water rushed into the “Control Cubico” or maneuvering room, the compartment just forward of the aft torpedo room. The watertight door between maneuvering and the aft torpedo room could not be closed because it was warped by the collision. The watertight door to the aft engine room was closed, however.

Unfortunately, the collision alarm was never sounded. Whether individuals on the bridge failed to sound the alarm or the alarm was not operational is unclear. Either way, the result was the same. Individuals forward of the “Control Cubico,” other than those on the bridge, were not aware that there had been a collision. Individuals began moving to the scene, both through the interior of the ship and via the forward hatch, moving aft topside. The true nature of events was revealed almost immediately, however, when PACOCHA began to assume an up angle.

1850 – 1853 Surface Escape.

One of the three individuals who perished in the water was responsible for closing the main induction valve. He failed to do so before abandoning ship. Hence, as soon as PACOCHA’s induction mast was below water both engine rooms also rapidly flooded. Fortunately, the watertight door between the forward engine room and the aft battery compartment had been secured. Otherwise, the entire ship might have flooded.

Three crewmembers, a lieutenant, a chief, and a petty officer, were trapped in the flooded compartments. Their bodies were recovered three weeks later.

The Captain of the ship, Commander Nieva, lost his life securing the bridge access hatch. Divers located his body the following morning inside the deck access door to the sail.

In the forward torpedo room, Lieutenant Cotrina, the senior survivor aboard, secured the forward torpedo room watertight door and began to blow air to the compartment. He then went to the forward torpedo room hatch to secure it. Instead, however, he had to force the hatch open to free a sailor whose leg was caught as the hatch fell closed due to the 40 degree up angle PACOCHA assumed before sinking below the surface. As the PACOCHA began her slide to the bottom, water rushed in the forward hatch, washing lieutenant Cotrina down the ladder, but fortunately, shortly afterwards, forcing the hatch closed. Lieutenant Cotrina considered this miracle.

1855 – PACOCHA: On the Bottom.

Survivors estimate the time lapse between collision and settling on the bottom to be no more than five minutes.

LT Cotrina secured the blow to the forward compartment, which he estimated lasted forty seconds from the time the forward torpedo room hatch closed until the blow was secured. Because of the pressure created, the watertight door leading aft could not be opened initially. When tried later it opened, suggesting that pressure equalized slowly, probably through valves and vents rather than across the door.

Meanwhile in main control, the ballast tank blow was secured. A strong odor of chlorine from the aft battery compartment prompted a check of all valves and vents to be sure water was not entering this, or any other compartments. The aft battery was disconnected and this compartment was sealed from the rest of the forward compartments.

1900 – Scheduled Return to Port

Initially, the failure of PACOCHA to return to port on time was not of great concern to watch personnel. She had been in radio communication less than an hour previously. She had surfaced and was transiting to port. But as time passed, concern grew, especially after several attempts to make radio contact failed.

Other ships and the Maritime Authority were contacted to see if anyone knew of PACOCHA’s whereabouts. At first no one had any information. Then a radio conversation between the KIOWA MARU and its agent in Lima, in which the KIOWA MARU stated that it may have hit another vessel, was passed to watch personnel.

2002 – Emergency Declared.

Maritime authority boats were dispatched to search along PACOCHA’s route. The tug JENNIFER II was sent to the KIOWA MARU to investigate.

2020 – Admiral Tirado Arrived at the Callao Naval Base and Assumed Command.

Following notification and arrival at his headquarters, Admiral Tirado dispatched the submarine DOS DE MAYO to search. As yet there was no hard evidence that PACOCHA was involved in a collision, let alone that she had been sunk.

2030 – PACOCHA: Released Messenger Buoy.

In addition to releasing their messenger buoy, those in the forward compartments of PACOCHA attempted to call aft compartments on the sound powered telephone. There was no response.

2050 – Collision Confirmed by JENNIFER II

Arriving at the KIOWA MARU, the personnel of the JENNIFER II had difficulty communicating with the Japanese crew. Initially, they were distracted from discovering the collision by requests to take one of the Japanese in SCUBA to the bow of the ship to investigate for damage. Eventually, they learned from a Peruvian fisherman, accompanying the Japanese as a guide, that there had been a collision with something. On the way into port, the KIOWA MARU had apparently gone a few hundred yards after the collision before coming to a stop in the water and then continuing into port unaware of what she struck.

2050 – Recall of Divers Commenced.

2050 – PACOCHA: Fired a Red Distress Flare.

As the JENNIFER II was reporting the collision on their radio, the collision area was illuminated by the first red distress flare fired from PACOCHA. The flare revealed many of the survivors in the water—but no boat. The fate of PACOCHA was now known.

2051 – Surface Survivors Rescued.

By 2100, many small boats from other ships were involved in the rescue effort. By 2240, twenty were rescued and three bodies were removed from the water. The last crewmembers rescued spent almost four hours in 14 degree Celsius (57 degrees Fahrenheit) water. Since only twenty-three crewmembers had been accounted for, surface search for survivors continued through the night. Those on the surface had no way of knowing that all remaining crewmembers were still aboard PACOCHA.

2100 – PACOCHA: Roll Call.

Survivors in the PACOCHA held a meeting in the forward torpedo room. A roll call was taken which revealed twenty-two survivors. Of these, there were four officers, four chiefs, and fourteen junior enlisted personnel.

Crewmembers were instructed to minimize activity. Many were wet and changed into dry clothes, which were obtained by opening lockers of crewmen normally berthed in the surviving compartments. Temperature in the boat was 21 degrees Celsius (70 degrees Fahrenheit). Contrary to expectations, the temperature actually rose over the next 24 hours to 25 degrees Celsius (77 degrees Fahrenheit), in spite of an estimated water temperature at depth of 11 degrees Celsius (52 degrees Fahrenheit).

2120 – PACOCHA: Fired Another Flare.

This flare led searchers to PACOCHA’s messenger buoy.

2131 – Messenger Buoy Located

Unfortunately, the messenger buoy on this class of submarine did not have a telephone, so communication could not be established with PACOCHA. Those on the surface realized, however, that someone was probably alive to release the buoy and fire the flare.

2145 – PACOCHA: Steinke Hood Training.

Training in the use of the Steinke Hood for escape was conducted. Crewmembers had received very little training in the use of the Steinke hood. The Peruvian Navy, like the U.S. Navy, stopped formal in-water escape training from depth several years previously. This change in Peru came after a sailor died during a training exercise.

2240 – The Last Survivors were Rescued from the Water.

Twenty-three personnel were accounted for. Unbeknown to the rescuers, the remainder of PACOCHA’s crew was in the submarine.

2250 – PACOCHA: Chlorine Gas.

The smell of chlorine gas in main control prompted another assessment of the boat’s condition. A vent valve was found that had not been tightly closed, and more water had seeped into the aft battery compartment. All lithium hydroxide canisters were brought forward, and the survivors sealed themselves in the forward torpedo room.

2330 – PACOCHA: Settled for the Night.

Two canisters of lithium were opened and spread on the upper bunks. They recognized that spreading the lithium hydroxide on lower bunks would have been more effective, but the lower bunks were damp. The crew was put to bed.

2330 – Admiral Anderson Notified of Potential Need for a Rescue System.

2345 – The Director of the Naval Hospital was Altered that Help Would be required.

Survivors Ashore.

By 2400 all twenty survivors and three bodies had been brought ashore. Survivors were taken to the nearby Naval Hospital. Although all were suffering from hypothermia, none had significant injuries. No subsequent deaths occurred among this group.

Saturday, 27 August 1988

0000 – Divers Arrived on Scene.

By midnight an assortment of vessels were on the surface including the submarine, DOS DE MAY; a torpedo retriever; a floating crane; and several small craft.

Only eight divers were initially located. Locating divers during their off-duty hours was hampered by the lack of telephones in many of their homes. They were now on scene ready to begin diving in SCUBA gear. Depth to the deck of the ship was between 125 feet aft and 110 feet forward, with the ship variably reported as having between a nine and fifteen degree up angle. The first team of divers followed the messenger buoy’s line, which had played out to a significant distance. Since it was not located directly over PACOCHA, a second line was tended straight down to the sail. The divers tapped on the hull and received a response from the forward compartment of the boat. Unfortunately, they were unable to interpret the tapping initially, since they were unfamiliar with the code used.

0040 – Request for U.S. Navy Assistance.

Admiral Tirado called Captain Schillingsburg, U.S. Defense Attaché, to request rescue assistance from the U.S. Navy. Short delays were encountered establishing communication between Admiral Tirado and Captain Schillingsburg and between Captain Schillingsburg and the Office of the Chief of Naval Operations (CNO).

Although Captain Schillingsburg did not have a file on the agreement between Peru and the US Navy to provide rescue assistance, the CNO watch officer was familiar with the agreement.

0100 – PACOCHA: Messages were sent to the Rescuers on the surface that the survivors should be able to survive for 48 hours.

0200 – PACOCHA: Reassessed the Boat’s Status.

Three volunteers donned OBA’s and walked through compartments as far aft as main control. The aft battery compartment was noted to have water over the deck, so it was not entered.

0200 – Salvage Air Connections.

Personnel ashore including several divers studied the salvage air connections on PACOCHA’s sister ship, LA PEDRERA (USS Sea Poacher SS406). Salvers discovered that they did not have salvage air hoses or fittings. Ultimately, MK-V diving system umbilicals were used with fittings manufactured during the night on two frigates. (MARK V Diving hoses are negatively buoyant, ½ inch inner diameter, 600-psig pressure rated hoses, U.S. MIL-H-2815)

0227 – Communications Established.

After two frustrating hours, improved communications with PACOCHA were finally established using the signal ejector to pass written notes to the divers. This pair of divers, the last of the initial group of eight, surfaced shortly thereafter. Each diver made one SCUBA dive, working in pairs, in wet suits to 110 feet for 20 minutes with a 3 minute decompression stop at 10 feet. None of the divers developed decompression sickness.

0350 – U.S. Navy Rescue System.

Word that the U.S. Navy was sending its rescue system brought great relief to those in charge of the rescue operation. Unfortunately, over the next few hours the estimated time of arrival of the rescue system shifted steadily to a later arrival time.

> 0420 – PACOCHA: Fired a Yellow Flare.

Not having had any communication from the surface for approximately two hours and unaware that there were currently no divers available, PACOCHA fired another flare. Yellow was picked so as not to give the impression that something new was seriously wrong ---they just wanted to express concern that they had not heard anything in a couple of hours.

0440 – PACOCHA: Fire in Control

Although details were not clear, a small electrical short/fire occurred in main control. Fortunately it was brief and self-extinguishing, but it was a new cause of concern for their atmosphere. Should there be a fire in their compartment, only carbon dioxide extinguishers were available.

0500 – Diving Resumed.

A new group of divers arrived on scene in the early morning. Ashore, they had reviewed salvage connections, escape trunk configuration, and other details on the PACOCHA’s sister ship, LA PEDRERA. Shortly after the divers went to work, they discovered and recovered the body of PACOCHA’s Commanding Officer, Commander Nieva, just inside the deck access door to the sail superstructure.

0600 – PACOCHA: Reveille.

Breakfast. Utilizing the signal ejector, communication was passed that the crew was in good spirits with enough air to last for seventy-eight hours based on calculations of available oxygen and lithium hydroxide. They also had adequate supplies of water, but no food after eating what little they had, including cake, for breakfast.

A heavy black cloud was noted to be rising from below the deck in the forward battery compartment. No one entered this compartment again. Two more canisters of lithium hydroxide were opened and spread on the upper bunks. Later in the morning another four canisters were opened. Approximately twenty canisters were unopened. One 8 cubic foot oxygen cylinder was bled into the compartment; three oxygen cylinders were left unused.

0630 – PACOCHA: Escape Training.

Information on the use of the escape trunk and the Steinke Hood was passed from the surface. The crew was divided into five groups and one member from each group trained in the operation of the escape trunk. Groups were arranged by seniority, with one officer in four of the five groups, and by other factors such as swimming ability and self-confidence.

0645 – PACOCHA: Survivors Identified.

Via message, PACOCHA informed those on the surface that there were twenty-two survivors.

0730 – U.S. Navy Rescue System.

A message was sent to PACOCHA informing them that the fly-away rescue system was on the way from the U.S. This provided a visible boost to morale among the crewmen.

0950 – PACOCHA: Atmosphere Deteriorating.

Lt. Cotrina became increasingly concerned about the submarine’s atmosphere when he noted that the crew was becoming listless, agitated, and hyperventilating. The lithium hydroxide did not seem to be doing the job. There fore, he spread four additional canisters. Unfortunately the boat’s only atmosphere monitoring equipment was aft in the flooded compartments. Their only light, the emergency light located at the bottom of the forward ladder, was periodically flickering on and off, and the beam from their only battle lantern was steadily growing weaker.

0950 – Permission to Escape.

When Lt. Cotrina requested guidance, Admiral Tirado granted permission for the senior man onboard PACOCHA to use his best judgment to decide if and when escape should be executed because of deteriorating conditions.

1000 – PACOCHA: Decision to escape

It was unanimous with one exception. One of the Lieutenants voiced his opinion against escape for various reasons. If he had to escape, he wanted the divers to provide scuba tanks since he had been trained in SCUBA. The senior officer placed him in the first group of escapees. Hence the first group to escape was a group of four, composed of two officers and two enlisted.

1130 – Salvage Air

Divers completed connecting high and low salvage using Mark V diving umbilicals for hoses and the manufactured fittings. The high salvage was connected to air bands on the submarine, ABTAO. These banks were charged by thirty-five year old, oil lubricated compressors. There are no filters on the system, and air samples of the air banks have never been taken. Lieutenant Cotrina briefly opened and air valve from PACOCHA’s air banks to the compartment to help circulate the air. He may have done so on other earlier occasions as well.

1130 – PACOCHA: Escape Group One.

During escape training, crew members decided to inflate their Steinke Hoods in the compartment before entering the escape trunk. For reasons that are unclear, they elected to use the Steinke Hoods as a flotation device, but not to enclose their heads in the hoods. One member of this group, Chief Monzon, did wear the hood. He was to be the third most seriously injured of the twenty-two escapees. After inflating the escape devices, the four entered the escape trunk (Appendix 4) and controlled flooding and pressurizing from inside the trunk. The water flooding the trunk was so cold that the escapees wee sure they would die. They were all extremely frightened. After the side access hatch was opened, they spent at least ten minutes arguing over who would exit first. Finally LT Gomez, the senior man, ducked under and began his ascent, he was followed in turn by Chief Monzon and Petty Officer Reyes.

LT Gomez described how he began blowing out, but fearing he would not have enough air to reach the surface, he held his breath for a moment, and then resumed breathing out again. He felt that his lungs were empty on arrival at the surface. After being on the surface for two or three minutes, he noted that his chest and neck felt “puffy.” He described what could be interpreted as crepitus in his neck. Not long thereafter, he developed considerable pain in both shoulders.

Both enlisted crewmen also surfaced and initially seemed to be in good condition. After several minutes, however, they too became symptomatic. They became disoriented and unsteady, and developed pains and shortness of breath.

The fourth member of the group, however, failed to surface. Since those on the surface had been told to expect four in the first group they began to search but held little hope for the fourth escapee. While they searched, those in the forward compartment drained and opened the escape trunk. They found the fourth member of the team alive and well, still in the escape trunk.

1215 – PACOCHA: Escape Group Two. Lieutenant Nieri and Three Enlisted Personnel.

This group completed their escape by 1225 hours without serious incident. Following an indeterminate delay, Lieutenant Nieri and possibly others in this group were flown by helicopter to the recompression chamber. Proper advice was given by Admiral Tirado, so that the helicopter flew low over the water. Further delay occurred before this group was recompressed, as the one usable chamber was in use.

Immediately after the second group surfaced, air was supplied through the high salvage connection. Aboard PACOCHA, water came from the line since it had not yet been blown dry. The high salvage was immediately secured from inside the ship and never reopened according to the senior officer on board, lieutenant Cotrina. Low salvage as best can be determined, terminated above the surface of the sea and was open to the atmosphere. It originated below the surface of the water in the bilge, and thus was filled with seawater to a depth equivalent to the pressure in the boat.

1230 – Escape Group 3. Five Enlisted Personnel.

All five of the survivors in this group completed an uneventful escape by 1240. Unfortunately, after this group left the escape trunk, the outer escape hatch could not be closed from inside the submarine. When the crew attempted to drain the trunk, seawater continued to flood into the submarine until the valves were secured. Attempts to drain the trunk were aborted when seawater had filled the bilge to the just below the deck, thus further increasing the pressure in the boat.

After their plight was communicated to the surface, divers were sent to investigate. Apparently one or more of the hatch’s dogs were obstructing closure. The divers eventually freed the obstruction with a large wrench.

1500 – Escape Group 4. Four Enlisted.

This group made an uneventful escape by 1515. On reaching the surface at least one of them was transported to the shore recompression facility by helicopter.

1615 – Escape Group Five. Lieutenant Cotrina and Two Non-swimmers.

Survivors in this group made an uneventful escape by 1625. By this time, a recompression chamber was on scene on the floating crane along with two medical officers. All three in this escape group were recompressed within five minutes of surfacing.

1710 – Escape Group 6. Lieutenant Lindley, Chief Bendezu and Petty Officer Grande.

After the fifth group left the escape trunk, divers placed a set of SCUBA bottles in the trunk. Whether this was in response to requests by Lieutenant Lindley is not clear. Possibly it was done because of increasing concern that the atmosphere was becoming contaminated. Whatever the rationale, the final three escapees spent between one-half and one hour breathing from the SCUBA bottles before escaping at 1805. The exact time of entering, flooding, and pressurizing the escape trunk is unknown.

During this time, personnel topside were again becoming apprehensive. Investigating divers were present when all three escapees simultaneously emerged from the top escape trunk hatch. Why they didn’t use the side hatch, as had the rest of the escapees is unclear.

Since the chamber at the scene was occupied, these individuals were transported by boat to the shore facility. About an hour and a half lapsed between surfacing and recompression, apparently because no chamber was available. Unfortunately one of the three, Petty Officer Grande, develop such severe decompression sickness, possibly combined with gas embolus, that he died during recompression treatment.


Survivability in a disable submarine depends upon many factors including oxygen levels, carbon dioxide levels, toxic gases, hypothermia, food, water, and atmospheric pressure in the Submarine.

Food and water is rarely a factor which will limit survivability, as evidenced in this case. Toxic gasses may have affected survival time. Whether significant amounts of chlorine gas had found its way into the forward compartment is unknown but the survivors, as a group, did not report lung irritation as a major complaint. Low oxygen levels may well be a factor in survivability, but usually not the limiting factor. High oxygen partial pressures can become toxic but it has been well demonstrated that humans can survive for at least 30days in compressed air at 60 psig. Thus that was not likely to have played a part in this scenario. The presence of other toxic agents in the air used to pressurize the compartment initially is possible but probably not as important as the ultimate carbon dioxide accumulation. Usually the limiting factor, especially if the submarine is pressurized, is elevation of the carbon dioxide level rather than hypoxia or other contaminants.

In a compressed air environment without replenishment, the partial pressure of carbon dioxide reaches critical levels before the oxygen partial pressure is significantly depleted and requires supplementation. LT Cotrina obviously understood the need to circulated and mix the air in the compartment to maximize mixing of the oxygen released from storage bottles and to enhance carbon dioxide removal by the movement of air across the Lithium Hydroxide. Unfortunately his resources for circulating the air were limited and he had no equipment to monitor the effectiveness of his efforts at atmosphere maintenance. It is possible that the small fire at 0440 hours in Main Control and the black smoke noted above the forward battery well at 0600 may both have been partly related to the increased partial pressure of oxygen and the related increase in fire hazard inherent in a compressed air environment. A release of stored energy from the forward batteries from a battery fire might partly explain the rise in temperature within the PACOCHA from 21 degrees to 25 degrees Celsius. Oxygen was apparently being added to the atmosphere at a rate calculated to match oxygen utilization by the survivors. Thus the atmosphere in the compartments should have approximated the oxygen content of compressed air. The amount of Lithium Hydroxide spread out was, in retrospect, apparently insufficient to keep up with the metabolic production of carbon dioxide by the survivors. It is probably wise to spread out as much carbon dioxide absorbent as surface areas will permit right from the beginning when trapped in this situation. Elevation of atmospheric pressure can multiply the physiological effects of the component gases. Addition of uncontaminated air will not change the partial pressure of Carbon Dioxide or any other component previously present in the compartment. Elevated pressure, however, will not significantly affect the rate at which the partial pressure of Carbon Dioxide in the compartment climbs as people breathe. Accumulation of Nitrogen in body tissues will occur at fairly predictable rates related to the partial pressure of Nitrogen, so that when escape or rescue occurs the survivors may develop decompression sickness.


Exact internal pressures and durations of those pressures in the forward torpedo room are unknown. Preparations were made from the beginning to mobilize all recompression chambers and personnel in the area for whatever contingencies developed. Certain information is now available allowing extrapolations and calculations to be made to estimate the variables of pressure and time.

a. As PACOCHA sank, water began to pour into the aft compartments of the boat via the rent in the pressure hull, the main induction valve, and the aft escape hatch. The watertight door between the forward engine room and aft battery compartment was closed early in the flooding before the forward hatch was closed. Thus flooding and attempts to pressurize the aft compartments probably contributed very little to pressurization of the forward torpedo room.

b. LT Cotrina freed a man’s leg from the side hatch of the forward escape trunk and attempted to close it as the boat sank. However, as the boat sank, water entering the hatch swept him out of the escape trunk before he could finish closing the hatch. LT Cotrina had ordered a high-pressure blow in the compartment as water came in and this lasted for 1 to 2 minutes before the increasing angle off the boat slammed the hatch. The blow then continued for about 40 seconds until it was secured after it was obvious flooding had stopped. Thus, pressure in the compartment was increased above 1 atmosphere from that time on.

c. One 8 cubic foot oxygen bottle was vented into the compartment during the time the men were trapped. Since the Carbon Dioxide absorbent (Lithium Hydroxide) was apparently not functioning well, the combination of unused Oxygen valved in plus the unabsorbed Carbon Dioxide produced may have contributed a small component to a pressure increase in the boat.

d. High and low salvage connections (Appendix 5) were completed at 1130 hours on 27 August, some 16 ½ hours after the sinking. However the lines were flooded when connected and naturally sent a stream of water into the boat when pressure was initially applied to the high salvage line. The men in the compartment then secured the valve on that connection and it was never opened again. The low salvage line was underwater in the compartment and, although it apparently remained open at the surface, obviously remained filled with water to a height in the hose equal to the internal pressure in the boat. At that point the hose either collapsed from external water pressure, (It was not an armored hose), or remained open and filled with air the remaining distance to the surface. I neither condition this did not allow air pressure to the surface. Had either line been dry and open between the compartment and the surface, pressure in the compartment would have fallen to 1 atmosphere. Thus the high and low salvage connections apparently did not contribute to any pressure changes in the compartment. Considering the number of cases of decompression sickness that developed when the escapees reached one atmosphere of pressure on the surface, it is fortunate that such a pressure reduction did not develop in the boat when the hose were connected.

e. The survivors cracked the valves from PACOCHA’s air banks to circulate the air in the compartment on at least one occasion and perhaps more often. This also contributed to increasing the compartment pressure.

f. The flooding and subsequent draining of the escape trunk (Appendix 4) during each of the first five escape evolutions added water to the internal volume of the forward torpedo room and that further increased the pressure. This effect was accentuated following the third group of escapees when the side hatch did not close properly and a large volume of water entered the boat when drain down of the escape trunk was attempted.

g. Four hours after the sinking the survivors noted that an incompletely secured vent valve had allowed water to flood the battery well in the aft battery compartment. This volume of water also increased the internal pressure in the forward compartments.

h. It was noted that initially, after pressurization of the forward torpedo room, the water-tight door leading aft to the forward battery compartment would not open. Later the pressure apparently equalized between the compartments and the door could be opened. It is not clear whether pressure leaked from the forward torpedo room into the aft spaces or whether pressure increased in the aft spaces by some other mechanism.

These factors were recognized by the survivors, but there was no recall of a gauge or manometer showing the actual pressure in the forward compartment. However, during conversations with LT Cotrina, who pressurized the escape trunk for the first four groups that escaped, one additional important fact materialized. When the trunk is pressurized to equalized pressure with surrounding water, in order to open the side escape hatch, air pressure is supplied from with the submarine. There was a pressure gauge on that line (Appendix 4) and it reads pressure in the line relative to that surrounding it in the boat. Since the escape trunk was at about 110 feet of sea water gauge (fswg) deep, it should have taken some 48.9 pounds per square inch gauge (psig) of pressure to equalize, assuming the boat were at surface pressure.

(Assuming 33 fswg – 1 atmosphere of pressure – 14.7 psig)
(110 fswg divided by 33 ft – 3.33)
(3.33 times 14.7 psig – 48.9 psig)

LT Cotrina, however remembered that the gauge was showing only 24 to 25 psig. A bit of additional calculations show that there may well have been approximately 54 feet of pressure in the boat at the time of the first escape.

(25 psig divided by 14.7 psig – 1.7 atmospheres)
(1.7 times 33 feet – 56 fswg of pressure needed to equalize)
(110 feet – 56 feet-54 fswg of pressure in the boat)

The duration of this pressure is not clear, but certainly the incidence of decompression sickness (a minimum of 20/22) certainly indicates the pressure calculated above may be reasonable at the time of the escape evolutions. The historical events suggest an elevated pressure in the compartment from the first few minutes a the submarine sank with at least some minor step increase as events transpired over the remaining hours of their entrapment.

Work in the United States and England on pressurized escape and rescue in recent years has led to information from which guidelines for escape and rescue in this type of situation have been recently formulated. The time limit for “No decompression” exposure at 54 feet is 60 minutes as set forth in the U.S. Navy Diving Manual (Appendix 6). Thus after 1 hour at 54 feet, an increasing decompression obligation had been incurred, whether they escaped or were rescued. Further, the additional exposure to 110-fswg pressure followed by rapid decompression during the escape procedure made the risk of decompression even greater. Recent recommendations derived from British and U.S. research show that at a depth of 110 FSWG, increasing exposures to pressures in excess of 1.7 atmospheres of pressure absolute (1.7 ata – 23 fswg) within the boat make it unsafe to escape rather than await rescue. The lack of guidelines and absence of a pressure gauge to show internal pressure within the submarine made those with the submarine, as well as those on the surface, unaware of the increasing hazard during buoyant escape as time passed. While the possibility of gas embolism had been anticipated, certainly no one on scene or in Peru had the information to anticipate the number and severity of decompression sickness cases that were to develop after the otherwise successful escapes.

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