Dorado Loss Scenario
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Background: Loss scenarios, facts, & other data
Introduction
Possible causes for Dorado's loss
Weather
Mechanical Failure or Operational Accident
- Stern planes jam dive - The stern diving planes, fashioned like horizontal rudders and located aft of the propellers, are used to control the angle of the boat while it is submerged. A failure of the mechanical or hydraulic systems that control and operate the planes could lead them to become stuck in the full dive position, pushing the boat into a steep dive and rendering it uncontrollable. Example: Chopper (SS-342), 1969. Probability: very low. Dorado was a new boat and had been extensively tested and inspected prior to departure.
- Valve failure - If a valve fails to operate or structurally fails under submergence pressure, rapid and possibly uncontrollable flooding can occur. Example: Squalus (SS-192), 1939. Probability: very low, for the same reasons listed above.
- Battery explosion and fire - Dorado was equipped with two 126-cell lead acid storage batteries, used to provide electricity to electric motors for submerged propulsion. The batteries have to be periodically recharged using the diesel generator sets, and this process is tricky and dangerous if not closely monitored and regulated. When charging, the battery cells can generate extremely flammable hydrogen gas, which if it builds up to high levels can generate an explosion. Related to this is the fact that the batteries can also generate very lethal chlorine gas if sea water is allowed to get into the cells. Every once in a while, this process goes wrong, with disastrous results. Example: Cochino (SS-345), 1949. Probability: medium to low. This is a well practiced procedure that the crew is thoroughly trained for. Most submarines charge their batteries several times a day without incident.
- Collision - A collision involving a submarine usually ends up in disaster for the sub. It will sink quickly due to its relatively low reserve buoyancy. Example: S-51 (SS-162) collision, 1925. Probability: very low. No reported collisions occurred anywhere along Dorado's route.
- Hull structural failure - Sometimes a submarine's hull can structurally fail under submergence compression, due to age, or due to unknown damage. The results are usually catastrophic. Example: S-28 (SS-133). Probability: negligible. Dorado was a brand new boat and had been fully tested to its maximum rated depth.
Any of these scenarios is indeed a possible explanation for Dorado's loss, and they can't be definitively ruled out until the wreck is found and surveyed. However, the authors are confident that none of them are the precipitating event that caused her loss, for reasons put forth throughout this page.
Attack by a U-boat
For these and other reasons outlined here, a direct attack by an enemy submarine on the Dorado can be definitively ruled out as a cause of her loss.
Mine strike
Once dropped from the tube the weapon would sink to the bottom. A hydrostatic switch would then activate, releasing the upper explosive mine from its weighted base, with the mine floating up on its cable to a pre-set depth where it would activate. It was supposed to remain moored via the cable to its base until detonated by a passing ship. The mines would be laid one at a time, at the prescribed interval to achieve the desired field shape. The delay in activation was intentional, allowing the U-boat to open enough distance so that the mine would not detonate from the effects of the U-boat's hull.
The points in black labeled A through J are the reported locations of the mines when they were detected and swept by U.S. forces. The data in the lower left gives the dates when the mines were found. The discrepancies in location are to be expected. U-214's plotting of the field was likely not as precise as they recorded it due to the limitations of navigation in that period (no GPS or precise electronic navigation systems). The same can be said for the recorded U.S. locations. It should also be noted that mine "A" (U.S.) does not necessarily correspond to mine "1" (German), etc.
There are several other very important data points on this chart. First, the first mine was discovered and swept by U.S. forces on October 9, Just three days after Dorado's departure from New London and while she was still well out in the Atlantic on her transit (see below). The presence of the mine field was already known prior to Dorado's scheduled arrival and it was actively being swept and neutralized.
Second, the prevailing currents in the area were to the east-northeast. Any mines that broke free of their mooring cables or had their cables cut by the minesweepers would have drifted on the currents in that direction, well out of the path that Dorado was following to Point George. Indeed, mine "I", swept on October 29 but not immediately destroyed, drifted northeast past Manzillo Point before it was finally neutralized.
Third, and most importantly, Point George, Dorado's final navigation waypoint and the spot she was to rendezvous with the USN destroyer on the surface, was seven nautical miles north of the northern most boundary of the minefield. Dorado could not possibly have contacted one of U-214's mines as they all laid to the south of the rendezvous position. After that point she was to proceed on the surface under escort of the destroyer and the two ships would have transited through an already swept lane to the submarine base at Coco Solo. Other than the detonations of the mines by the minesweepers as they were being neutralized, no underwater explosions were reported by any of the numerous ships in the area, an indication that a submarine had contacted a mine.
At 2135 (7:35 pm) on the evening of October 12, 1943 the U-214 deployed one of these mines in a position southwest of Dorado, and generally in the path she needed to take to get to Point George. The datum point for this deployment was roughly 40 nautical miles from Dorado's position at the time, and the prevailing currents in the area would have the EMS mine drift on a divergent course east-northeast and out of the Dorado's way.
Assuming that Dorado made it that far, the chances of her running into this small, singular floating mine in the vastness of the central Caribbean is infinitesimal at best. While this remains a viable theory, we rate its probability as negligible to zero.
Friendly fire
The Loss Scenario
The Departure
She passed under the U.S. Route 1 bridge, with the venerable structure lifted open to allow the boat to pass underneath. She passed the main Electric Boat facility on her port beam, and a little further downstream she passed the Victory Yard where she was built. Men and women toiling in the cool October air on Dorado's sister subs paused for a moment, proudly acknowledging their handiwork as the submarine passed. They wished her luck as she headed off to war.
The crew was experiencing a mixed set of emotions. They had come to enjoy their stay in Connecticut and had a deep appreciation for the hard work put forth on their behalf by the Electric Boat personnel. Friendships had developed with the workers that the men valued. Some of the crew had brought family members to the Groton/New London area and they were now leaving that all behind; a touch of sadness prevailed as they sailed down the Thames River. There was also a palpable sense of anxiety as they pushed the bow of the boat into the unknown. The experienced men knew of the combat that laid ahead, the inexperienced men put on a brave face as they tamped down their fears. All of that was tempered by the excitement of finally moving forward. They were well trained and confident in themselves and their shipmates, and despite lingering anxiety they eagerly anticipated the adventure that laid ahead.
Fishing vessels hailed her as she passed the mouth of the Thames and Schneider rang up an ahead standard bell with turns for 14 knots. The bridge watch team kept a wary eye on the Fisher's Island and Montauk ferries as they passed, with a little maneuvering left and right intended to keep the ferries at a safe distance. Clearing Fisher's Island she made a slight turn to the southeast, putting her on course to pass down the middle between Montauk Point on her starboard side and Block Island on her port. Down below in the conning tower and control room the Quartermasters and the Navigator were busy piloting the submarine, shooting bearings with the periscope to land-based navigation aids, using those bearings to triangulate their position on the chart. With Montauk Point on their starboard quarter, they took their "point of departure", i.e. the last confirmed land-based navigational fix, and headed out into the blue Atlantic.
The Voyage
The final waypoint was Point George, 15 nautical miles (NM) north of the Cristobal Breakwater, a structure that defined the harbor for Cristobal and Colon. At George the Dorado was to rendezvous with a U.S. destroyer, who would escort Dorado on the surface the last few miles to the submarine base. This rendezvous was supposed to happen at 1100 local (11:00 am) on the morning of October 14. This date/time is very important for several reasons:
- Being escorted into the harbor by the destroyer would prevent Dorado from being mistaken for a German submarine (known to be operating in the Caribbean) and being fired upon by friendly forces. Being early or late for the rendezvous was frowned upon, as it would cause serious tactical, operational, and logistical problems that the Navy wanted to avoid.
- Traffic through the canal was very high, and specific times were assigned to ships for passage so that the possibility of traffic jams was avoided. If Dorado missed her transit time, it would delay her voyage all the way to Pearl Harbor and the war zone and exacerbate the operational and logistical issues previously mentioned.
- The date/time of her arrival at Point George also dictated the speed of her transit, known properly as her "speed of advance" (SOA). To make Point George on time her SOA was 14 knots. This was also a fuel efficient speed and was well within her maximum surface speed of 21 knots. However, it also dictated that Dorado make the transit mostly on the surface, as her maximum submerged speed was only eight knots. LCDR Schneider had the discretion to submerge as he saw fit for drills and training, but he had to maintain the average speed of 14 knots in order to make George on time.
Dorado would also make the voyage under a condition known as "radio silence". This was a procedure in which Dorado was not to use her radio for routine transmissions, out of a concern that German submarines in the area might use those transmissions to triangulate her position. The crew could receive broadcasts, and Schneider had the latitude to report serious circumstances if he felt it was warranted, but things like routinely reporting her position and administrative message traffic was not allowed.
The zone was big enough to allow the zig-zag course to be conducted, and for periodic dives for training and drills. However, it was incumbent upon the crew of Dorado to ensure they stayed within the zone at all times. Allied surface and aerial forces were understandably a bit on edge due to the threat of German submarines, and this zone was intended to eliminate the "friendly" threat to U.S. submarines transiting to Panama.
Prelude: October 11 and 12, 1943
Around mid-day on October 11, the boat was approaching Point Dog, and they raised Cape Engano on the eastern tip of the island of Hispaniola right on time. They proceeded apace through the Mona Passage between the Dominican Republic and Puerto Rico, passing through Point Easy and out into the Caribbean. Dorado's base course between Points Easy and Fox was 243° true, or southwesterly, with the zig-zag plan having Dorado jinking left and right of that course.
The critical 13 minutes: 2039-2052, October 12, 1943
Upon detection of the surface target on radar, Felix continued to fly the PBM on its southerly course of 190° true. His intention was to visually acquire the target in order to make an evaluation. Sure enough, at eight nautical miles out the faint silhouette of a small ship was seen with binoculars in the bright moonlight. Felix immediately made a turn to the right. The intention was to swing around and place the target "up moon", that is silhouetted with the moon in the background. That would give his crew the maximum visibility of the target while at the same time hiding their approach in the black background.
He moved to his left and glanced at the gyrocompass repeater in front of the helmsman and saw that they were steady on course 310° true. The OOD was dutifully following the zig-zag plan and they were now to the right of their base course of 243° and temporarily headed northwest. He turned to the right and grabbed the rungs of the ladder to the bridge. Squeezing up through the open hatch, he was greeted by the Officer of the Deck announcing, "Captain on the bridge."
Lieutenant Felix came out of the wide sweeping left turn and steadied up on course 090°, or due east and steadied at an altitude of 1000 feet. At 2049 at a range of three nautical miles, both pilots and another crewman stationed at the nose gun station were able to confirm that the target was indeed a submarine. The sighting was fleeting, just a few seconds. Felix faced a dilemma, should he attack or try to confirm identity? Quickly mulling it over he realized that everything he had been briefed on, everything that he had trained for, and all of the information that the had told him that this was a German U-boat. He made the decision to attack. He begins a slow descent to release altitude at a speed of 170 knots.
Fortunately, Schneider's eyes were already adapted to the dark. He had been wearing red lens goggles while resting in his cabin, and red lights were on in the forward battery and control room compartments, preventing night blindness. About four minutes had elapsed since he had arrived on the bridge, and he was diligently scanning the skies with binoculars, along with the two lookouts, the Officer of the Deck, and one Quartermaster. A call came up from the conning tower, "Bridge, radar. Aircraft contact now intermittent. Last good range 8000 yards". To Schneider this meant that the inbound aircraft was descending to the minimum altitude that the SD radar could track it, 1000 feet. Two seconds later, "Bridge, radar. Aircraft contact lost." Suddenly, the port lookout calls out, "Aircraft contact, three points on the port bow." Schneider swings around to the left, raises his binoculars, and peers intently into the blackness. A few seconds later he catches a faint moving shadow, close to the horizon, and the dim flashes of engine exhaust from two engines. He immediately thought "Looks like a PBM". Despite knowing this was a friendly aircraft, he was immediately wary. "Don't like the look of this", he thought.
Time had slowed for Schneider, and he stared at the approaching shape for what seemed like minutes, but was actually just three seconds. "Nope," he thought, "Don't like this at all." He pushed past the OOD and reached for the diving alarm switch. Turning slightly to his left he bellowed "Clear the Bridge" and pulled the diving alarm switch twice. The "aaoogahs" of the diving alarm jolted everyone awake below and initiated the maneuver that they had practiced repeatedly. Schneider's call of "Dive, dive" over the 1MC general announcing circuit backed up the urgency and instantly main ballast tanks vents were opened, engines were shut down, intake and exhaust valves shut, and the bow planes were rigged out. Schneider counted men as they jumped down the hatch, waiting until he was satisfied that all on the bridge were below. As he half fell, half climbed down the ladder himself he grabbed the hatch lanyard and pulled the hatch shut behind him, with the Quartermaster reaching up and dogging the hatch down tight. He yelled down the hatch to the control room, "Diving Officer, make your depth 200 feet smartly". He then ordered, "Helm all ahead flank". Back aft in the maneuvering room the electricians on watch positioned large switch levers to line up the two batteries in series, greatly increasing their voltage output, and they cranked the speed rheostats for the motors against their stops. Schneider felt the satisfying downward tilt of the deck and quietly muttered, "This is going to be close..."
No sooner had the words come out of his mouth when a loud WHANG preceded a jump in the deck, and the whole boat rattled. The 100 lb bomb had struck the aft part of the conning tower fairwater and although it did not detonate, it had enough kinetic energy to wreck the man-sized main air induction and main ventilation valves enclosed there. One second later the boat was pummeled by the nearly simultaneous detonations of two of the depth charges. Men were thrown to the deck, the lights went out, and the crew struggled to regain control as they nosed downward.
What happened to the Dorado at this point is very difficult to ascertain. Any number of circumstances could have befallen the boat, but the lack of wreckage and an oil slick on the surface means that at least she departed the surface intact. Predicated on the FACT that Dorado never made her rendezvous at Point George on the afternoon of October 14, some of the post-bombing scenarios may include:
- Dorado was not damaged at all. Schneider makes a hard left turn to clear the attack datum point while simultaneously speeding up and getting the boat down to a safe depth. She then sinks later due to an unrelated equipment casualty.
- Dorado suffered some equipment derangement, possibly including a loss of electrical power, possibly including a "jam-dive" on the stern diving planes, etc. The crew loses control of the boat and she sinks below crush depth.
- A combination of the two above. Dorado suffered some damage, i.e. flooded engine induction piping, jam-dive on the stern planes, etc., but was able to fight the damage and keep the boat going for perhaps up to a half-hour or more, before succumbing to the circumstances and sinking.
Ultimately, it will require that the wreck be found and surveyed before many of these questions can be answered.
Conclusions
More to come, work in progress.
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Thaddeus Weaver & David Johnston
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