Operation Deadlight was the Royal Navy's executive action which led to the sinking of 116 German U-Boats off the coast of Northern Ireland and Donegal between 27 November 1945 and 12 February 1946.
This was the culmination of the long-held determination of the British Government to ensure the total elimination of the German Navy’s submarine fleet after the end of WW2.
The Royal Navy therefore pressed ahead in the first half of 1944 with the detailed planning for the post-war transfer of all remaining German U-Boats to British ports. It was intended that the U-Boats would be moved to the naval port at Lisahally, and to the naval anchorage in Loch Ryan in south-west Scotland.
The proposed transfer arrangements were code-named Operation Pledge.
On 4 May 1945 the German Navy had ordered all U-Boats to cease operations and return to Norwegian ports. This was superseded on 8 May when the Admiralty ordered all U-Boats to surrender, and for those at sea to head for designated reception ports; the prime one of which was Loch Eriboll in north west Scotland. As a result, 156 U-Boats surrendered on both sides of the Atlantic.
Of the 156 U-Boats that had surrendered either from sea or in ports at the end of the European War (plus the one that had been interned in Spain), 138 were transferred to Lisahally and Loch Ryan to await decisions on their final disposal. Of the remainder, nine had surrendered from sea in Canada, the USA and Argentina, and 10 were unseaworthy in European ports.
Thirty U-Boats were to be allocated to each of the UK, the USA and the USSR, but a decision was deferred about the fate of the unallocated submarines. This was taken at the 18th Meeting of the Commission on 29 October, when it was agreed that all unallocated submarines were to be sunk in the open sea in a depth of not less than one hundred metres by not later than 15 February 1946.
Thus, of the 135 U-Boats moored in Loch Ryan and at Lisahally, eight were allocated to the UK, one to the USA and 10 to the USSR. This left 116 U-Boats at Lisahally and in Loch Ryan awaiting final disposal by the Royal Navy. This therefore led to Operation Deadlight.
As the remaining 116 U-Boats were to be sunk at sea, it was decided that the disposal action should be initiated without delay. This was not only to meet the deadline of 15 February 1946, but also because the imminent onset of winter and its associated rough seas in the area to the north west of Loch Ryan and Lough Foyle would make the towing and scuttling of the U-Boats a hazardous task.
As a result, Operation Deadlight was initiated immediately after the Tripartite Naval Commission’s 18th Meeting on 29 October.
On 31 October, the Admiralty instructed the RN Commander-in-Chief at Rosyth to begin making the detailed arrangements for the disposal of the unallocated U-Boats.
With the aim of completing the exercise as soon as possible, the initial planning meeting to determine the necessary actions was held at Pitraevie in Fife on 5 November, and the formal order for Operation Deadlight was issued on 14 November; it being defined as a plan for scuttling 110 U-Boats from Loch Ryan (86) and Lisahally (24) in deep water off the north west coast of Ireland, starting on 25 November.
The omission of six U-Boats from the list in Annex A of the Deadlight Operation Order has caused considerable confusion ever since, despite the UK’s 1946 Naval Estimates (Cmd 7054) giving the correct figure of 116.
The six U-Boats missing from Annex A, which were all moored at Lisahally, were U-975, U-1023, U-2351, U-2356, U-2502 and U-3514 and, in each case, there were ongoing discussions about their possible inclusion in the lists of those U-Boats to be allocated to the Allies.
It had been agreed by the Tripartite Naval Commission that there should be a degree of flexibility and that bi-lateral exchanges of individual ships and craft between the Allies could be made as desired.
Thus, there are a number of differences between the original lists of the U-Boats allocated to each of the three Allies and those that were finally implemented. Because these six U-Boats were all included in the initial allocation lists, they were therefore omitted from Annex A.
However, ultimately they did not feature in the final allocations, and were therefore added to the original list of 110 unallocated U-Boats after the Deadlight Operation Order was published.
Of the 116 U-Boats, 86 were moored in Loch Ryan and 30 were tied up to pontoons at Lisahally, and they comprised 1 type IID, 73 type VIICs, 1 type VIID, 1 type VIIF, 11 type IXCs, 4 type IXD2s, 4 type XXIs and 18 type XXIIIs.
The 30 U-Boats which were sunk during Operation Deadlight, having been berthed at Lisahally, were:- U-244, U-278, U-294, U-363, U-516, U-541, U-668, U-764, U-802, U-825, U-861, U-874, U-875, U-883, U-901, U-930, U-975, U-1010, U-1022, U-1023, U-1109, U-1165, U-2336, U-2341, U-2351, U-2356, U-2502, U-2506, U-2511 and U-3514.
The aim of Operation Deadlight was that all the U-Boats should be towed (unmanned) to a designated position 130 miles to the north west of Lough Foyle, where they would then be sunk.
The prime method was to be by the use of demolition charges, however if weather conditions allowed, a number of U-Boats were to be sunk by RAF and Fleet Air Arm aircraft, and others were to be sunk by RN submarines.
If any of these methods of disposal failed, then the U-Boats were to be sunk by gunfire.
As expected, the weather was particularly bad in November and December 1945, and the planned disposal arrangements did not work on the majority of occasions, especially as far as the plans for sinking the U-Boats with demolition charges were concerned.
There were also major problems with the towing of the unmanned, unmaintained and, in many cases, almost unseaworthy U-Boats.
Comparison of the planned disposal arrangements with what actually happened shows the scale of disruption wrought by the weather.
Only two of the U-Boats were sunk by demolition charges, only seven by submarines and only 13 by aircraft. Of the remainder, almost 50% foundered under tow before they ever reached the designated scuttling area.
These either sank directly or were sunk by gunfire, some of them in positions very close to the entrances to Loch Ryan and Lough Foyle. The remainder were sunk by gunfire, as it was far too dangerous to follow the pre-planned demolition procedure.
During Operation Deadlight 28 of the U-Boats from Lisahally were sunk between 29 December 1945 and 9 January 1946, and the remaining two U-Boats (U-975 and U-3514), which were two of the late additions, were sunk on 10 and 12 February 1946 respectively.
The sinking of the 116 U-Boats and the completion of Operation Deadlight on 12 February 1946 marked the end of virtually all of the Kriegsmarine's surviving serviceable U-Boats which had surrendered at the end of WW2 in Europe.
The Allies had been allocated 30 for technical purposes, one had been returned to Holland (UD-5), two others (U-805 and U-1228) had been sunk off the west coast of the USA in early February 1946, and a further eight unseaworthy U-Boats remained in continental ports (one in France and seven in Norway).
Thus, the long-held determination of the British Government to ensure the elimination of the German submarine fleet had been achieved.
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