Convoy SC 107

Convoy SC 107 was the 107th of the numbered series of World War II Slow Convoys of merchant ships from Sydney, Cape Breton Island to Liverpool. The ships departed New York City on 24 October 1942 and were found and engaged by a wolfpack of U-boats which sank fifteen ships.Hague 2000 p.135 It was the heaviest loss of ships from any trans-Atlantic convoy through the winter of 1942–43.Hague pp.132, 137–138, 161–162, 164, 181 The attack included one of the largest non-nuclear man-made explosions in history, when torpedoed ammunition ships SS ''Hobbema'' and SS ''Hatimura'' - both were sunk, one exploded, with the German submarine also being destroyed in the explosion.

Background

As western Atlantic coastal convoys brought an end to the "Second Happy Time", Admiral Karl Dönitz, the ''Befehlshaber der U-Boote'' (''BdU'') or commander in chief of U-Boats, shifted focus to the mid-Atlantic to avoid aircraft patrols. Although convoy routing was less predictable in the mid-ocean, Dönitz anticipated that the increased numbers of U-boats being produced would be able to effectively search for convoys with the advantage of intelligence gained through ''B-Dienst'' decryption of British Naval Cypher Number 3. However, only 20 percent of the 180 trans-Atlantic convoys sailing from the end of July 1942 until the end of April 1943 lost ships to U-boat attack.

Discovery

''B-Dienst'' decrypted message traffic detailing routing and composition of convoy SC 107, and fifteen U-boats of wolfpack ''Veilchen'' (violet) were deployed to intercept it. The convoy was found and reported by , patrolling the same general area as wolfpack ''Veilchen'', on 29 October as the Western Local Escort ForceRohwer & Hummelchen 1992 p.170 turned the convoy over to Escort Group C-4,Milner 1985 p.290 supported by the convoy rescue ship ''Stockport''. obtained a HF/DF bearing when ''U-522'' sent the first convoy contact report at 16:24, and the convoy made a course change after dark in the hope of evading the shadowing U-boat.Waters, pp.31–34 Soon after, a No. 10 Squadron RCAF Digby bomber sunk , patrolling in the area of the convoy. As the boats of ''Veilchen'' were sailing towards their assembly point, wolfpack boat was sunk by a RCAF Lockheed Hudson. Wolfpack boat found the convoy and released ''U-522'' to sail off for other prey.

First attack on 1/2 November

''Stockport'' and ''Restigouche'' located 25 HF/DF transmissions from the eight U-boats in contact with the convoy on the afternoon of 1 November, but the single destroyer was unable to investigate all of them. At sunset HMS ''Celandine'' was sent to investigate the closest HF/DF fix eight miles off the port quarter; and ''Restigouche'' made a sweep astern. After sunset, a clearing sky revealed the flickering ''aurora borealis'' to port silhouetting the convoy and its three remaining escorts. As ''Restgouche'' engaged an ASDIC contact six miles behind the convoy with depth charges and star shells, nervous merchant sailors revealed the convoy location by firing snowflake pyrotechnic mortars.Waters, pp.38–55

While ''Restigouche'' pursued another U-boat, ''Kapitänleutnant'' Siegfried von Forstner's passed the destroyer at 22:40 while overtaking the silhouetted convoy from astern. When corvette had a radar malfunction, ''U-402'' went undetected as it penetrated the starboard side on the convoy screen about midnight to torpedo the British freighter ''Empire Sunrise''. ''Empire Sunrise'' fired two flares and most of the ships in convoy fired snowflake mortars. ''U-402'' dived to avoid the rapidly approaching ''Restigouche'' whose depth charges were comfortably distant. ''Restigouche'' narrowly avoided torpedoes launched a short time later by as the convoy changed course 40 degrees to port to confuse the U-boats.

While ''Celandine'' dropped astern to screen ''Stockport'' rescuing survivors from ''Empire Sunrise'', ''U-402'' twice more penetrated the convoy screen where ''Celadine'' had been and torpedoed the Greek freighter ''Rinos'' and British freighters ''Dalcroy'', , and ''Empire Leopard''. ''U-402'' was lightly damaged by machine-gun fire from corvette and by a projectile from a merchant ship. ''Kapitänleutnant'' von Forstner would receive the Knight's Cross of the Iron Cross for his work in ''U-402'' during this convoy and in Convoy SC 118 on the next patrol. ''U-522'' torpedoed the Greek freighter ''Mount Pelion'' and British freighters ''Hartington'' and ''Maratima''. During the melee, merchant ships avoided two torpedoes launched by , three from , and four from ; while ''Arvida'' avoided damage from machine-gun fire by several merchant ships who thought she might be a U-boat.

2 November

Rain and misty weather caused the U-boats to lose contact after ''U-522'' torpedoed Greek freighter ''Parthenon'' in a daylight attack. Escort Group C-4 was reinforced by the V-class destroyer from convoy HX 213 before nine U-boats regained contact when visibility improved on 3 November.

Second attack on 3/4 November

''Celandine'', ''Amherst'' and ''Vanessa'' attacked the gathering U-boats unsuccessfully while the convoy reassembled after losing cohesion in the fog. One of the straggling merchant ships avoided two torpedoes launched by ''U-438''.Waters, pp.60–72 ''U-521'' torpedoed the American tanker ''Hahira'' shortly after dawn on 3 November. ''Stockport'' was carrying 350 survivors by the time she picked up those from ''Hahira''. Harbor tugs and had been attached to the convoy for passage to Iceland, and were detailed to act as rescue ships because ''Stockport'' was carrying three times her intended capacity. The little tugs were ordered to keep their running lights on in their assigned rescue positions astern of the convoy to minimize chances they might be mistaken for U-boats. torpedoed the convoy commodore's freighter ''Jeypore'' after sunset on 3 November; but snowflake illumination was minimal because most ships had exhausted their supply of pyrotechnics during the earlier attacks. Corvettes and made unsuccessful counterattacks before torpedoed the Dutch freighter SS ''Hobbema'' and British freighters ''Empire Lynx'' and ''Hatimura'' at 23:10. The entire convoy and nearby U-boats were shaken thirty minutes later by a heavy explosion believed to have been one of the largest prior to atomic bomb testing. The magnitude of the explosion temporarily stopped the engine of the rescue tug six miles astern of the convoy and caused several ships to believe they had been torpedoed. ''Titus'' was abandoned before the captain realized she was undamaged and returned with a skeleton crew including survivors from other ships. U-boats submerged at a depth of 200 feet reported being severely jolted, and ''U-132'' is believed to have been destroyed by the detonation. The cause of the explosion was undetermined, but assumed to have resulted from detonation of the ammunition cargo of either ''Hobbema'' or ''Hatimura'' while they were sinking.

On 4 November, ''Arvida'' and ''Celandine'' were detached to Iceland with ''Stockport'' and the two tugs overcrowded with a total of 590 survivors. ''U-89'' torpedoed the British freighter ''Daleby'' shortly before the convoy escort was reinforced by the United States Coast Guard cutter and the s and from Iceland. No. 120 Squadron RAF B-24 Liberators scrambled from Iceland drove off the remaining U-boats, and the convoy reached Liverpool on 10 November.

Ships in convoy

German losses

RCAF bombers, patrolling the area of Convoy SC 107, sunk the free-patrolling on 30 October and wolfpack ''Veilchen'' member on 5 November. Wolfpack ''Veilchen'' boat sunk herself through the explosion caused by her torpedoing of ''Hobbema'' (or ''Hatimura'') on 4 November.

See also

* Convoy Battles of World War II
* Operation CHASE for a description of experimental detonation of obsolete munition cargoes in sinking ships to simulate nuclear testing.

Notes

References

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* {{cite book , last=Waters , first=John M., Jr. , title =Bloody Winter , publisher =D. Van Nostrand Company , date =1967 , location =Princeton NJ

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Naval battles of World War II involving Canada
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