Convoy HG 73

{{main|Ultra (cryptography)}}

The British Government Code and Cypher School (GC&CS) based at Bletchley Park housed a small industry of code-breakers and traffic analysts. By June 1941, the German Enigma machine Home Waters ({{lang|de|Heimish}}) settings, used by surface ships and U-boats, could quickly be read. By mid-1941, British Y-stations were able to receive and read {{lang|de|Luftwaffe}} W/T transmissions and warn of Luftwaffe operations. In June and August several convoys were routed around U-boat wolfpacks, reducing sinkings in August to {{cvt|80000|LT}}.{{sfnm|1a1=Macksey|1y=2004|1pp=141–142|2a1=Hinsley|2y=1994|2pp=141, 145–146|3a1=Budiansky|3y=2013|3p=192}}

{{main|B-Dienst}}

The rival German {{lang|de|Beobachtungsdienst}} ({{lang|de|B-Dienst}}, Observation Service) of the {{lang|de|Kriegsmarine}} and the {{lang|de|Marinenachrichtendienst}} (MND, Naval Intelligence Service) had broken several Admiralty codes and cyphers by 1939. In 1941, B-Dienst read signals from the Commander in Chief Western Approaches informing convoys of areas patrolled by U-boats, enabling the submarines to move into these "safe" zones.{{sfn|Kahn|1973|pp=238–241}} In September 1941, despite more escorts, convoy losses increased during delays in breaking Enigma, if U-boats were near enough to a convoy. On 11 September the Germans disguised grid coordinates by coding them separately and for weeks U-boat orders could only be guessed at.{{sfn|Winton|1988|pp=113–114}}

{{main|Kriegsmarine|Luftwaffe}}

File:Celtic Sea and Bay of Biscay bathymetric map-en.svg

To assist the Axis land forces in North Africa and to guard against British landings at Algiers and Oran {{lang|de|Oberkommando der Marine}} (OKM, Grand Admiral Erich Raeder) ordered that along with six U-boats sent to the Mediterranean in September, U-boat attacks were to be made on British convoys to Egypt via Gibraltar. Karl Dönitz, {{lang|de|Befehlshaber der U-Boote}} (BdU, Commander of the U-boats) opposed these orders because the Gibraltar to Britain convoys and their reciprocals were a sideshow compared to the North Atlantic and because most British supplies went around Africa rather than through the Mediterranean. Attacks on Convoy HG 70 and Convoy HG 71 did not inspire optimism, given the number of surface escorts and the extent of air cover that the U-boats had to overcome. Only the best U-boat captains could hope to succeed and even then, the obstacles were formidable.{{sfn|Blair|1997|pp=388–389}}

According to Dönitz, the best U-boat commanders were needed in the North Atlantic, the decisive theatre of the U-boat tonnage war. A compromise was agreed in that attacks on Gibraltar convoys would continue but with smaller wolfpacks of about eight submarines each, searching much further into the Atlantic where RAF Coastal Command patrols were less frequent and there was the possibility that OS (Outbound South) convoys to Sierra Leone and WS (Winston Specials, troop convoys) might be found. U-boats in the area could be reinforced temporarily by U-boats en route to the North Atlantic or returning to France. Focke-Wulf Fw 200 Condor long-range reconnaissance bombers based at Bordeaux would search for the convoys.{{sfn|Blair|1997|pp=388–389}}

File:Bundesarchiv Bild 146-1978-043-02, Focke-Wulf Fw 200 C Condor Recolored.jpg

For three weeks, no OG and SL convoys were found and wolfpacks {{lang|de|Bosemüller}} with seven U-boats and {{lang|de|Kurfürst}} with eight submarines failed to sink any ships. U-boats and aircraft sighted convoys but the British ability to read U-boat signals encyphered with the Enigma machine allowed them evasively to route the convoys away from the wolfpacks in atrocious weather. U-boats sailed for France or to other operations and the remainder formed wolfpack {{lang|de|Seewolf}} but this also came to nothing. {{GS|U-95||2}} and {{GS|U-561||2}} were attacked on 14 September by aircraft from Coastal Command and severely damaged, forcing them to abandon the wolfpack. {{lang|de|Seewolf}} was disbanded and then northbound ships of Convoy HG 73 were spotted by an Italian submarine west of Gibraltar. Three U-boats were in striking distance but {{GS|U-371||2}} was en route to the Mediterranean and was ordered to press on.{{efn|U-124 was a Type IX U-boat usually thought to be too big, too slow-diving and lacking in manoeuvrability for operations against convoys with plenty of escorts.{{sfn|Blair|1997|p=389}}}} U-371 passed Convoy HG 73 and sent a sighting report which allowed {{GS|U-124||2}} and {{GS|U-201||2}} to close on the convoy. Searching {{cvt|600|nmi}} west of the English Channel, observers on U-124 saw smoke on the horizon on 20 September. The convoy found by U-124 was Convoy OG 74 from Britain. BdU ordered Mohr to shadow the convoy and direct U-201 towards it.{{sfn|Blair|1997|pp=388–389}}

File:The Royal Navy during the Second World War A11648.jpg

Convoy OG 74 comprised 27 ships with an escort of the 36th Escort Group, the escort carrier, {{HMS|Audacity|D10|6}}, the sloop {{HMS|Deptford|U53|6}}, five corvettes including {{HMS|Marigold|K87|6}}, {{HMS|Arbutus|K86|2}} and the Ocean Boarding Vessel {{HMS|Corinthian||2}}. The convoy was shadowed until the night of 20/21 September when both U-boats attacked. U-124 obtained three hits from three torpedoes and claimed two ships and a tanker but sank only the small merchant ships Baltallin (1,303 GRT) and Empire Moat (2,922 GRT). The convoy illuminated the night with snowflake star shells which were particularly bright, forcing U-124 to submerge and retire. On 22 September as the two U-boats moved to positions from which to resume their attacks during the night and KG 40 sent Condors to attack the convoy. F4F Wildcats (Martlets in British service) from Audacity attacked the Condors and shot one down; one Martlet strafed U-124 or U-201, forcing it to dive but another Condor seriously damaged the rescue ship Walmer Castle (906 GRT) that had stopped to rescue survivors from Baltallin and Empire Moat and had not caught up with the convoy and was sunk by Marigold. The two U-boats attacked after dark on both flanks of the convoy. Three ships were sunk and City of Waterford (1,017 GRT) was lost in a collision with Thames. After four ships for Lisbon were detached, U-201 sank Runa (1,575 GRT), Lissa (1,511 GRT) and Rhineland.{{sfnm|1a1=Hague|1y=2000|1p=177|2a1=Woodman|2y=2005|2pp=378–379}}

File:Gibraltar World Wind view annotated.jpg

Convoy HG 73 comprised 25 ships homeward bound from Gibraltar, some in ballast and others carrying trade goods. The convoy commodore was Rear-Admiral Kenelm Creighton in the cargo liner Avoceta and the convoy was protected by a Western Approaches Command escort group consisting of the sloop {{HMS|Fowey|L15|6}} and eight corvettes, reinforced by the auxiliary cruiser and CAM ship (catapult aircraft merchant ship) {{HMS|Springbank||6}}. The convoy sailed from Gibraltar on 17 September 1941 and German agents across the bay in neutral Spain reported its composition, escort strength and departure time. Condors from Kampfgeschwader 40 (KG 40) from Bordeaux and the Italian submarines {{ship|Italian submarine|Leonardo da Vinci|1939|2}}, {{ship|Italian submarine|Alessandro Malaspina||2}}, {{ship|Italian submarine|Morosini||2}} and {{ship|Italian submarine|Luigi Torelli||2}} on patrol west of Gibraltar were ordered to search for the convoy, while three U-boats further north were deployed in a search patrol line across the convoy's probable route.{{sfn|Rohwer|Hümmelchen|2005|p=101}}{{efn|Malaspina had been sunk, possibly by a Sunderland of 10 Squadron RAAF on 7 September.{{sfn|Rohwer|Hümmelchen|2005|p=101}}}}

On 18 September a Condor sighted Convoy HG 73 off Cape St Vincent; Springback opened fire with its 4-inch anti-aircraft guns, which forced the Condor to open the range. Petty Officer F. J. Shaw the Fulmar pilot (804 Naval Air Squadron of the Fleet Air Arm) launched from Springbank but the Condor escaped by flying at wave-top height. Shaw returned after half an hour to report that the Condor was too fast; he could parachute into the water or attempt the flight to Gibraltar and chose the latter, landing safely.{{sfn|Terraine|1999|pp=383–384}} This left the convoy with no means to attack a Condor that appeared next morning.{{sfn|Woodman|2005|p=380}} On 19 September the convoy was sighted again, first by Morosini and later by U-371, though both lost contact; Morosini fell out of the pursuit with engine trouble and U-371, en route to the Mediterranean, was ordered to continue on her way.{{sfn|Rohwer|Hümmelchen|2005|p=101}} On 20 September the destroyers Duncan and Farndale departed and were replaced by destroyer {{HMS|Wild Swan|D62|6}}.{{sfn|Kindell|2024}}

File:HMS Highlander(H44).jpg

Convoy HG 73 was attacked by the Italian boats and on the night of 21/22 September; Vimy attacked a contact and damaged Torelli. On 22 September Vimy and Wild Swan, left the escort, replaced by the destroyer {{HMS|Highlander|H44|6}}.{{sfn|Kindell|2024}}

On 23 September Da Vinci made contact and shadowed the convoy throughout the day but was unable to attack.{{sfn|Rohwer|Hümmelchen|2005|p=101}} On 24 September a Condor spotted the convoy and reported three ships on fire, though British records show no ships hit. BdU diverted U-203 and U-205 to the attack from France; these arrived over the next two days. On 25 September U-124 made contact in heavy seas and fired on a ship identified as a cruiser; this may have been Springbank but no hits were achieved, Empire Stream was sunk and the survivors rescued by Brgonia, six mambers of the crew and two stowaways being lost. That night U-203 joined and both U-boats attacked, just after midnight U-203 sank Varengberg and Avoceta but came under attack from the corvette {{HMS|Larkspur|K82|6}}. A few hours later U-124 sank Cortes and Petrel, Lapwing stopped to pick up survivors from these two ships but was torpedoed just before dawn. Of the 109 men on the three ships only 18 men survived, reaching land after a two-week voyage in an open lifeboat.{{sfn|Woodman|2005|pp=380–382}}

File:Western Approaches.PNG}}]]

On 26 September, Highlander departed from the escort, while U-124 and U-203 continued to shadow. U-201 and U-205 also joined. During the day U-205 was attacked and damaged by an Allied aircraft forcing a return to base. During the night of 26/27 September the three U-boats in contact attacked; just before midnight U-124 sank Siremalm and at {{nowrap|2:00 a.m.}} U-201 torpedoed and sank Cervantes and Springbank, whose survivors were taken off and then Jasmine sank the ship with gunfire rather than leave her as a hazard. During 27 September the three U-boats continued to shadow and that night U-201 made a final attack, sinking Margareta. The U-boats were obliged to abandon the operation and return to base to re-arm.{{sfn|Rohwer|Hümmelchen|2005|p=101}} Convoy HG 73 sailed on without further incident, arriving at Liverpool on 1 October.{{sfn|Blair|1997|pp=389–391}}

Of the 25 ships that departed Gibraltar nine were lost (36 per cent) and an escort vessel was sunk. Of the 177 convoys of the HG series run during the three years between September 1939 and September 1942, thirteen (just over one in ten) were attacked. Of the ships convoyed, 44 (about 20 per cent) were lost.{{sfn|Hague|2000|pp=177–179}} The operation was a victory for the {{lang|de|Luftwaffe}} and {{lang|de|Kriegsmarine}}. The three U-boat commanders who had sunk ships were credited with the destruction of fifteen ships, of 91,000 GRT; the three ships spotted sinking on 24 September were credited to Malaspina, which had failed to return. (In 1997 Clay Bliar wrote that the three ships did not appear in British records.){{sfn|Blair|1997|p=390}} The nine ships sunk amounted to 25,800 GRT.{{sfn|Blair|1997|p=390}}

{{notelist}}

{{reflist|20em}}

{{refbegin}}

• {{cite book |last=Blair |first=Clay |title=Hitler's U-boat War: The Hunters 1939–1942 |volume=I |year=1997 |orig-year=1996 |publisher=Weidenfeld & Nicolson |location=London |isbn=0-297-84076-2}}
• {{cite book |last=Brown |first=David |title=Warship Losses of World War Two |year=1995 |orig-year=1990 |publisher=Arms and Armour Press |location=London |edition=2nd rev. |isbn=978-1-85409-278-6}}
• {{cite book |last=Budiansky |first=Stephen |title=Blackett's War: The Men Who Defeated the Nazi U-boats and Brought Science to the Art of Warfare |year=2013 |publisher=Alfred A. Knopf |location=New York |edition=e-book |isbn=978-0-307-96263-8}}
• {{cite book |last=Hague |first=Arnold |year=2000 |title=The Allied Convoy System 1939–1945: Its Organisation, Defence and Operation |publisher=Chatham |location=London |isbn=1-86176-147-3}}
• {{cite book |last=Hinsley |first=F. H. |series=History of the Second World War, United Kingdom Military Series |title=British Intelligence in the Second World War: Its Influence on Strategy and Operations |location=London |publisher=HMSO |year=1994 |orig-year=1993 |edition=2nd rev. abr. |isbn=978-0-11-630961-7}}
• {{cite book |last=Jordan |first=Roger W. |title=The World's Merchant Fleets 1939: The Particulars and Wartime Fates of 6,000 Ships |year=2006 |orig-year=1999 |publisher=Chatham/Lionel Leventhal |location=London |edition=2nd |isbn=978-1-86176-293-1}}
• {{cite web |last=Kindell |first=Don |title=HG Convoys: Convoy HG.73 |url=http://www.convoyweb.org.uk/hg/index.html?hg.php?convoy=73!~hgmain!~tagmain |year=2024 |website=convoyweb |access-date=9 September 2024}}
• {{cite book |title=The Searchers: Radio Intercept in two World Wars |last=Macksey |first=K. |author-link=Kenneth Macksey |year=2004 |orig-year=2003 |publisher=Cassell |location=London |edition=Cassell Military Paperbacks |isbn=978-0-304-36651-4}}
• {{cite book |last=Kahn |first=D. |title=The Codebreakers: The Story of Secret Writing |year=1973 |orig-year=1967 |publisher=Macmillan |location=New York |edition=10th abr. Signet, Chicago |oclc=78083316 |lccn=63-16109}}
• {{cite book |last1=Rohwer |first1=Jürgen |first2=Gerhard |last2=Hümmelchen |title=Chronology of the War at Sea, 1939–1945: The Naval History of World War Two |year=2005 |orig-year=1972 |publisher=Chatham |location=London |edition=3rd rev. |isbn=978-1-86176-257-3}}
• {{cite book |last=Terraine |first=John |author-link=John Terraine |title=Business in Great Waters |year=1999 |orig-year=1989 |publisher=Leo Cooper |location=London |edition=Pbk. repr Wordsworth Editions, Ware |isbn=1-84022-201-8}}
• {{cite book |last=Winton |first=John |title=Ultra at Sea: How Breaking the Nazi code affected Allied Naval Strategy during World War II |year=1988 |publisher=Sapere Books |location=Leeds |edition=e-book |isbn=978-1-80055-522-8}}
• {{cite book |last=Woodman |first=Richard |title=The Real Cruel Sea: The Merchant Navy in the Battle of the Atlantic, 1939–1943 |year=2005 |orig-year=2004 |publisher=John Murray |location=London |edition=Pbk. |isbn=0-7195-6599-5}}

{{refend}}

• {{cite book |last=Creighton |first=Kenelm |title=Convoy Commodore |year=2017 |orig-year=1956 |publisher=Arcole |location=Pittsburgh, PA |edition=ePuB |pages=124–136 |isbn=978-1-78720-921-3}}
• {{cite book |last=Hague |first=Arnold |year=2000 |title=The Allied Convoy System 1939–1945 |publisher=Vanwell Publishing |location=St. Catharines, Ont. |isbn=1-86176-147-3 |ref=none}}
• {{cite book |last=Kemp |first=Paul |title=U-boats Destroyed: German Submarine Losses in the World Wars |year=1997 |publisher=Naval Institute Press |location=Annapolis, MD |isbn=978-1-85409-515-2}}
• {{cite web |last=Kolbicz |first=Rainer |title=Convoy HG 73 |year=2024 |url=https://uboat.net/ops/convoys/convoys.php?convoy=HG-73 |website=uboat.net |access-date=9 September 2024}}
• {{cite web |last=Kolbicz |first=Rainer |title=Convoy HG-73: Reassessment of U-boat attacks during the nights of 25/26 and 26/27 September 1941 |year=2009 |url=https://uboat.net/articles/index.html?article=71 |website=uboat.net |access-date=9 September 2024}}
• {{cite book |series=History of the Second World War United Kingdom Military Series |title=The War at Sea 1939–1945: The Defensive |volume=I |last=Roskill |first=S. W.|author-link=Stephen Roskill |editor-last=Butler |editor-first=J. R. M. |editor-link=James Ramsay Montagu Butler |year=1957 |orig-year=1954 |publisher=HMSO |location=London |edition=4th impr. |url=http://www.ibiblio.org/hyperwar/UN/UK/UK-RN-I/index.html |access-date=18 April 2018 |oclc=881709135}}
• {{cite book |last=Niestlé |first=Axel |title=German U-boat losses During World War II: Details of Destruction |year=2014 |publisher=Frontline Books |location=London |edition=ebook |isbn=978-1-4738-3829-1}}

• [http://www.convoyweb.org.uk/hg/index.html Convoy HG 73 at Convoy Web]
• [https://uboat.net/ops/convoys/convoys.php?convoy=HG-73 Convoy HG 73 at U-boat net]

{{World War II}}

{{DEFAULTSORT:HG073}}

Category:North Atlantic convoys of World War II

C

Category:Naval battles of World War II involving Germany