Convoy HG.73
Part of the Battle of the Atlantic of the Second World War
Map of the Bay of Biscay
Date 17 September – 1 October 1941 Location North Atlantic Result Axis victory
Belligerents
Kriegsmarine  Regia Marina	United Kingdom
Commanders and leaders
Karl Dönitz	Kenelm Creighton
Strength
5 U-boats 3 Italian submarines	25 merchant ships 16 escorts
Casualties and losses
	10 ships sunk 301 killed

Convoy HG 73 (17 September – 1 October 1941) was a trade convoy of merchant ships during the Second World War. It was the 73rd of the numbered HG convoys Homeward bound to the British Isles from Gibraltar. The convoy departed Gibraltar on 17 September 1941 and was spotted by a German reconnaissance aircraft on 18 September. The convoywas attacked over the next ten days. Nine ships were sunk from the convoy before the submarines exhausted their torpedo inventory on 28 September. The convoy reached Liverpool on 1 October.

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 (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 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 80,000 long tons (81,000 t).^[1]

The rival German Beobachtungsdienst (B-Dienst, Observation Service) of the Kriegsmarine and the 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.^[2] 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.^[3]

To assist the Axis land forces in North Africa and to guard against British landings at Algiers and Oran 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, 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.^[4]

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.^[4]

For three weeks, no OG and SL convoys were found and wolfpacks Bosemüller with seven U-boats and 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 Seewolf but this also came to nothing. U-95 and U-561 were attacked on 14 September by aircraft from Coastal Command and severely damaged, forcing them to abandon the wolfpack. 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 U-371 was en route to the Mediterranean and was ordered to press on.^[a] U-371 passed Convoy HG 73 and sent a sighting report which allowed U-124 and U-201 to close on the convoy. Searching 600 nmi (1,100 km; 690 mi) 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.^[4]

Convoy OG 74 comprised 27 ships with an escort of the 36th Escort Group, the escort carrier, HMS Audacity, the sloop HMS Deptford, five corvettes including HMS Marigold, Arbutus and the Ocean Boarding Vessel Corinthian. 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.^[6]

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 and eight corvettes, reinforced by the auxiliary cruiser and CAM ship (catapult aircraft merchant ship) HMS Springbank. 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 Leonardo da Vinci, Alessandro Malaspina, Morosini and Luigi Torelli 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.^[7][b]

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.^[8] This left the convoy with no means to attack a Condor that appeared next morning.^[9] 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.^[7] On 20 September the destroyers Duncan and Farndale departed and were replaced by destroyer HMS Wild Swan.^[10]

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.^[10]

On 23 September Da Vinci made contact and shadowed the convoy throughout the day but was unable to attack.^[7] 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. 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.^[11]

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 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.^[7] Convoy HG 73 sailed on without further incident, arriving at Liverpool on 1 October.^[12]

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.^[13] The operation was a victory for the Luftwaffe and 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.)^[14] The nine ships sunk amounted to 25,800 GRT.^[14]

Merchant ships (data from Kindell [2024] unless indicated)^[10]

Name	Year	Flag	GRT	Notes
Avoceta	1923	United Kingdom	3,442	Convoy Commodore, sunk U-203 26 September, 47°57'N, 24°05'W[15][c]
Cervantes	1919	United Kingdom	1,810	Sunk U-201 27 Sep, 48°37′N, 20°01′W, 8 dead, 32 survivors[17]
Cortes	1919	United Kingdom	1,374	Sunk U-124 26 Sep, 47°48′N, 23°45′W, 36 killed[18]
Coxwold	1938	United Kingdom	1,124
Cressado	1913	United Kingdom	1,228
Ebro	1920	Denmark	1,547
Empire Lake	1941	United Kingdom	2,852
Empire Stream	1941	United Kingdom	2,911	Sunk U-124 25 Sep, 6 crew, 2 stowaways killed[9]
Finland	1939	United Kingdom	1,375
Lanarhone	1928	Ireland	1,221	Bound For Dublin
Lapwing	1920	United Kingdom	1,348	Straggler, sunk U-203 26 Sep, 26 dead[d]
Leadgate	1925	United Kingdom	2,125
Margareta	1904	United Kingdom	3,103	Sunk U-201 27 Sep, crew rescued by Hibiscus.[20]
Marklyn	1918	United Kingdom	3,090
Meta	1930	United Kingdom	1,575
Panos	1920	United Kingdom	4,914
Penhale	1924	United Kingdom	4,071
Petrel	1920	United Kingdom	1,354	Sunk U-124 26 Sep, 26 killed[21]
Rudby	1924	United Kingdom	4,846
Siremalm	1906	Norway	2,468	Sunk U-201 26 Sep, 49°05'N, 20°10′W all 27 killed[22]
Spero	1922	United Kingdom	1,589
Starling	1930	United Kingdom	1,320
Switzerland	1922	United Kingdom	1,291
Vanellus	1921	United Kingdom	1,886	Vice-Convoy Commodore
Varangberg	1915	Norway	2,842	Sunk by U-203 26 Sep, 47°50'N, 34°50'W, 21 killed, 6 survivors[23]

Escorts^[10]

Name	Flag	Type	Dates	Notes
HMS Begonia	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Duncan	Royal Navy	D-class destroyer leader	17–20 September 1941
HMS Farndale	Royal Navy	Hunt-class destroyer	17–20 September 1941
HMS Fowey	Royal Navy	Shoreham-class sloop	17–30 September 1941
HMS Gentian	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Hibiscus	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Highlander	Royal Navy	H-class destroyer	22–26 September 1941
HMS Jasmine	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Larkspur	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Myosotis	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Periwinkle	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Springbank	Royal Navy	Fighter catapult ship	17–27 September 1941	Torpedoed 2:10 a.m., 27 Sep 1941 U-201[e]
HMS Stonecrop	Royal Navy	Flower-class corvette	17–30 September 1941
HMS Vimy	Royal Navy	V-class destroyer	17–22 September 1941
HMS Wild Swan	Royal Navy	W-class destroyer	20–22 September 1941
HMS Wolverine	Royal Navy	W-class destroyer	28 Sept – 1 Oct 1941

Axis submarines and Luftwaffe^[25]

Name	Flag	Class	Notes
Leonardo da Vinci	Kingdom of Italy	Marconi-class submarine	BETASOM (acronym of Bordeaux Sommergibili)
Alessandro Malaspina	Kingdom of Italy	Marconi-class submarine	BETASOM Sunk 7 September by RAAF Sunderland[7]
Morosini	Kingdom of Italy	Marcello-class submarine	BETASOM
Luigi Torelli	Kingdom of Italy	Marconi-class submarine	BETASOM, damaged night 21/22 by Vimy[7]
U-124	Kriegsmarine	Type IXB submarine	Sank four ships[7][26]
U-201	Kriegsmarine	Type VIIC submarine	Sank three ships[7]
U-203	Kriegsmarine	Type VIIC submarine	Sank two ships[27]
U-205	Kriegsmarine	Type VIIC submarine	Damaged by Coastal Command aircraft[7]
U-371	Kriegsmarine	Type VIIC submarine
Kampfgeschwader 40	Luftwaffe	Focke-Wulf Fw 200 Condor	Long-range reconnaissance bomber

• Creighton, Kenelm (2017) [1956]. Convoy Commodore (ePuB ed.). Pittsburgh, PA: Arcole. pp. 124–136. ISBN 978-1-78720-921-3.
• Hague, Arnold (2000). The Allied Convoy System 1939–1945. St. Catharines, Ont.: Vanwell Publishing. ISBN 1-86176-147-3.
• Kemp, Paul (1997). U-boats Destroyed: German Submarine Losses in the World Wars. Annapolis, MD: Naval Institute Press. ISBN 978-1-85409-515-2.
• Kolbicz, Rainer (2024). "Convoy HG 73". uboat.net. Retrieved 9 September 2024.
• Kolbicz, Rainer (2009). "Convoy HG-73: Reassessment of U-boat attacks during the nights of 25/26 and 26/27 September 1941". uboat.net. Retrieved 9 September 2024.
• Roskill, S. W. (1957) [1954]. Butler, J. R. M. (ed.). The War at Sea 1939–1945: The Defensive. History of the Second World War United Kingdom Military Series. Vol. I (4th impr. ed.). London: HMSO. OCLC 881709135. Retrieved 18 April 2018.
• Niestlé, Axel (2014). German U-boat losses During World War II: Details of Destruction (ebook ed.). London: Frontline Books. ISBN 978-1-4738-3829-1.

• Convoy HG 73 at Convoy Web
• Convoy HG 73 at U-boat net