The events around 14 September 1966
On Monday 12 September a group of ships of the Bundesmarine´s Ubootlehrgruppe (ULG) which consisted of the Tugboat Passat and the submarines Hai (shark), Hecht (pike) and U 3 put to sea from it´s base in Neustadt on the Baltic Coast of Schleswig-Holstein on a friendly visit to the Royal Navy base in Aberdeen in Scotland. The tender Lech joined the group in Kiel. Roughly once in a year ULG units set out for friendship visits in more distant ports as opposed to the only short training runs in Lübeck Bay and the western baltic. The men of the ULG called this almost mockingly “Fleet excursions”, but always were happy to go on such a trip.
The group was commanded by Commander Mahrholz, an experienced officer and veteran of the Battle of the Atlantic. It´s course led through the Kiel Canal. After reaching the open North Sea on 13 September the group split up: U 3 and Passat took a western course while Hai, Hecht and Lech steered a north-western course towards Heligoland. Wind and Seas were still moderate, after compensating for the higher water density of the North Sea waters resulting from higher salinity the submarines continued to travel North-West submerged. Around 01:15 am on Wednesday 14 September U Hai surfaced to charge it´s batteries. During the 12-hour dive weather conditions considerably worsened so the submarine dived again when recharging was complete to march submerged.
Not until around 05 pm the boat surfaced again. On 05:45 pm the tender Lech had the last radio contact with U Hai. As after 4 hours radio contact could not be reestablished the Lech reported this to the Navy Headquarters in Glücksburg and began searching for U Hai. Less than two hours later Navy Headquarters deployed the destroyer Bayern to the search. The Bayern was still undergoing final trials and was not yet fully operational.
Around 10:45 pm ropes that were washed out of it´s containers in the external casing of the conning tower by the sea got entangled in U Hecht´s propeller rendering it unable to manoeuvre. Lech headed towards U Hecht and tried to take it into tow with it´s Radar inoperative. Not until the next morning the Lech was actually able to take U Hecht into tow. On the initiative of naval aviators of the Bundesmarine on 03:44 am a maritime patrol aircraft started from an airbase at Kiel-Holtenau to search for U Hai while there was no greater concern for U Hai at the Navy Headquarters.
Only through a SOS call by the English fishing vessel St. Martin, that it had picked up a shipwrecked German submarine crew member the German navy learned that U Hai had sunk. Flimsy Hopes to find surviving crew members in air pockets in the wreck remained unfulfilled as there was no answer to rescue crew´s knocking signs. On 19 September the floating crane Magnus III raised the wreck of U Hai.
The assessment for the public prosecutors office
In an investigation against persons unknown for the suspicion of negligent homocide of crew members of the submarine U Hai the responsible public prosecutors office at the district court Lübeck ordered a written appraisal on the cause of sinking and an assessment of the boat´s seaworthiness from an expert committee, exclusively formed for for this case. This committee comprised of 7 Persons with representatives of the construction and reconstruction shipyards, of the Navy, of the Ministry of Defense and an retired submarine construction engineer, Christoph Aschmoneit. His submarine related estate kept at the U-boat Archive contains an original executed copy of this assessment.
The committee was already present at U Hai´s lifting and closely examined the wreck after it had been brought to a shipyard in Emden. The pressure hull was found to be completely watertight eliminating the possibility that a leakage was the cause of the sinking. After accounting for the salvage damages and recovering the bodies of seven crew members, the filling levels of all oil, trim and ballast tanks as well as all valve positions were recorded. Also the interior of the wreck was examined closely.
On 5/6, 25 and 26 October practical diving and trimming experiments to clarify the cause of the sinking with the sister boat U Hecht were made in the port basin of the naval armory Kiel. On 23 December the expert committee presented their written appraisal to the public prosecutors office in Lübeck.
The committee came to the assessment that there was practically no risk of capsizing for submarines of the German type 240. Although it had a limited range of courses and speed levels which could be used in heavy seas to prevent extreme rolling angles it seemed not conceivable to the committee that even in heavy seas a submarine of type 240 with intact technical systems and their appropriate operation simply sinks.
During a reconstruction in 1963 the U Hai and U Hecht´s pressure hulls were lengthened by 4 feet to accommodate the same diesel-electric propulsion System that also was used on the newly constructed German submarine type 201. The Diesel air intake pipe was shortened, connected to the snorkel through an air intake nozzle and blind flanged. On the surface the Diesel air intake either could take place through conning tower hatch and the boat´s interior or through the retracted snorkel, the air intake nozzle and the open Diesel air intake valve. Air intake through the conning tower hatch, however, caused a considerable draft inside the boat. If the hatch had to be closed due to overcoming seas it had to be re-opened virtually instantly as the vacuum resulting from the Diesel´s air consumption would extremely impede opening the hatch later.
On the stormy evening of 14 September with wind speed of 9 Bft and waves between 16 and 20 feet U Hai´s Diesel received it´s air intake through the retracted snorkel. The air intake nozzle did not completely fit on the retracted snorkel, so that every time it was washed over by a wave, water poured in the engine room bilge through the air intake pipe. It can be assumed that the engine room bilge was bailed after surfacing. The air intake duct ended close to the floor plating so that the Diesel operator would have had to stand up from his post to monitor the outlet of the air intake duct. In addition, pieces of clothing hung up to dry close to the outlet obstructed the view. Since there was only brief water ingress every time a wave washed over the air intake nozzle and moreover this could not be heard due to the noise of the engine and the swell, this successive water ingress seems to have been completely unperceived on U Hai.
The boat came down by the stern through the loss of buoyancy by the water ingress in the engine room. The air intake nozzle, which was roughly four feet above the water line in calm seas and with a trimmed boat, approximated the water line and was thus washed over by waves longer. By this more and more water flooded into the boat. In addition the stern ballast tank lost buoyancy by the escape of compressed air through the flood flap valve at the bottom of the tank when it was out of the water in the swell. The loss of buoyancy by the water ingress, however, was ten times higher than that by this escape of compressed air.
The expert committee´s practical experiments with the sister-boat U Hecht suggested that a water ingress of 5 m³ with the water level 3 inches below the floor plating could hardly remained unnoticed by the Diesel operator. According to the only survivor, out of the blue water ingress in the engine room was reported. Roughly 3 minutes later the order to abandon ship was given. The snorkel was equipped with a quick-action flap valve capable of stopping the water ingress. Though it was closed shortly before the sinking, the boat already was so down by the stern and deep in the water that it flooded through the conning tower hatch. In the opinion of the expert committee the available bailing capacities should have been sufficient to cope with the penetrated water and prevent a sinking, if the crew had established a clear to dive condition, in which all valves and hatches are closed and Diesel is shut down, rather than to abandon the boat. That the commanding officer of U Hai chose to abandon the boat can only be explained by a total unawareness on the cause of the water ingress leading him to regard stopping or reducing it as pointless. Establishing a clear to dive condition would yet have eliminated the option to instantly abandon the boat. No distress call could be sent.
Approximately 13 out of 20 men of U Hai´s crew reached the conning tower, but some of them were washed back into the boat by an overcoming wave. Silbernagel initially survived with group of 6 men, who all except of him died of hypothermia in the following hours. Not until 13 hours in the water later he was rescued by the English fishing cutter St. Martin as the only survivor.
The report of the Average Commission
From 13 January 1969 on the sinking of U Hai briefly came back to public awareness by an increased number of newspaper articles. This had started by an indiscretion by naval personnel towards a journalist from Kiel on an internal report of a marine inquiry board of the German navy named Average Commission and presided by rear admiral (lower half) Otto Kretschmer and a newspaper article on this. This commission was tasked with investigating the military, operational and civil law aspects of U Hai´s sinking and found considerable shortcomings in military procurement, training and personnel management of the German submarine fleet. Thereupon Kretschmer voiced fierce criticism in a German newspaper regarding German naval authorities and queried the qualification of U Hai´s commanding officer. Only a few days later he was barred from giving any further disclosures to the press by the Inspector of the Navy vice admiral Jeschonnek.
The Ministry of Defence rejected the deficiencies and reproaches mentioned in the report of the Average Commission. Nevertheless at the request of the then opposition party FDP the background of U Hai´s sinking and the report of the Average Commission, which was neither published nor submitted to any authority outside the navy were brought before the defense committee of the German parliament. A full and complete clarification of the accident´s causes and consequences by the German government and the publishing of the report of the average commission was demanded not only by the FDP but also from among the CDU/CSU´s coalition partner SPD. Even setting up a committee of inquiry was taken into consideration, but it was not performed in the end. The public prosecutors office in Kiel also considered a renewed investigation but did not initiate proceedings.
The remembrance of U Hai
Shortly after the accident a memorial stone was placed at the ULG´s naval base in Neustadt. When the ULG was restructured, renamed and relocated to Eckernförde in 1990 the memorial stone was taken along. On the initiative of the naval association “Marinekameradschaft Neustadt” a new memorial stone was place on a cemetery in Neustadt in 2005 through private donations and the help of the German Submariners Association as well as the evangelical parish Neustadt.
Former crew members have comradely meetings since 1994 and the informative homepage https://www.unterseeboot-hai.de/, alas in German only.
Assessment of the expert committee on the sinking of U Hai, 23 December 1966.
Text: Kai Steenbuck – pictures: Deutsches U-Boot-Museum, Roland.h.bueb