The route of the HG series of convoys from Gibraltar to Liverpool took them within range of Luftwaffe FW 200 ('Condor') aircraft acting both in a reconnaissance role, able to guide U-boats operating out of the French Atlantic ports onto the convoys, and as effective bombers against shipping. Despite the difficulties most convoys completed successfully, but of the 570 merchant ships which took part in the 28 separate convoys in 1941 on this homebound route 25 were lost, together with a further 5 stragglers. Experience in the other direction (designated OG) could be a little different because Germany was denied the intelligence information on sailings available from agents in Spain for the homebound stretch - 1004 ships took part in 30 OG convoys in 1941, with 21 lost in convoy, though a further 34 losses were classified as stragglers. 1941 was by far the most dangerous year for convoys on this route in either direction.
Convoy HG 73 saw the heaviest losses of all. A total of 25 merchant ships formed the convoy from Gibraltar on 17 September, together with an unusually strong escort including a destroyer and Fighter Catapult ship, although as usual most escorts were Flower class corvettes. Hastily brought together for the task, the escorts' lack of training as a team was subsequently blamed by C-in-C Western Approaches, Admiral Noble, for their lack of success. In retrospect, though, the convoy was unlucky to have been subject to concerted attack from three of the most able U-boat commanders of the war. The convoy seems to have been spotted by a FW 200 off Cape St Vincent and shadowed by U-371 and a group of three Italian submarines for several days whilst a U-boat pack was assembled. On 24 September a FW 200 established contact and guided U-124 and U-203 to the location. U-201 and U-205 joined later although U-205 was attacked on 27 September and damaged, and was unable to press home any effective attack. The other U-boats withdrew after expending all their torpedoes.
The following merchant ships were lost from the convoy:
| date | time | ship | gross registered tonnage | built | nationality | cargo | lives lost | sunk by |
|---|---|---|---|---|---|---|---|---|
| 25 Sept | 0744 | Empire Stream | 2 911 | 1941 | British | 3 500 tons potash | 8 | U-124 |
| 26 Sept | 0031 | Avoceta | 3 442 | 1923 | British | 88 passengers 469 tons general cargo |
123 | U-203 |
| 26 Sept | 0031 | Cortes | 1 374 | 1919 | British | general cargo | 31 | U-124 |
| 26 Sept | 0031 | Varangberg | 2 842 | 1915 | Norwegian | 4 100 tons iron ore | 21 | U-203 |
| 26 Sept | 0223 | Lapwing | 1 348 | 1920 | British | 750 tons pyrites & cork | 24 | U-203 |
| 26 Sept | 0223 | Petrel | 1 354 | 1920 | British | 405 tons general | 22 | U-124 |
| 26 Sept | 2303 | Margareta | 3 103 | 1904 | British | 400 tons general | 0 | U-201 |
| 26 Sept | 2335 | Cervantes | 1 810 | 1919 | British | 500 tons potash 400 tons cork |
8 | U-201 |
| 27 Sept | 0211 | Siremalm | 2 468 | 1906 | Norwegian | iron ore | 27 | U-201 |
HMS Springbank was one of a new type of Fighter Catapult Ship developed to counter the threat from land based aircraft. Originally constructed for merchant service in 1926, she was taken up into RN service in 1940 and converted into an anti-aircraft ship with a formidable armament including 8-4 inch (100 mm) guns in four twin HA turrets and two sets of quadruple 2 pounder pom-poms. In March 1941 she was fitted with a cordite powered catapult amidships mounted with a Fulmar two seater naval fighter. In the course of her duties with HG 73 her Fulmar aircraft was launched on 18 September and the enemy aircraft was attacked but escaped; when the aircraft arrived at Gibraltar it was discovered that faulty ammunition had caused all but one of the guns to jam. HMS Springbank was torpedoed at 0208 on 27 September by U-201. HMS Jasmine went alongside to take off survivors and after unsuccessfully attempting to sink her with depth charges did so by shelling.
U-124 was a type IXB ocean-going submarine built by Deschimag. She was launched 9 March 1940 and commissioned on 11 June. Under (then) Kapitänleutnant Johann Mohr she was an outstandingly successful boat; Mohr himself being awarded the Knights Cross with Oak Leaves. Earlier in the same patrol as the attack on HG 73 she spotted the outward bound convoy OG 74 and was responsible for the sinking of two ships from that convoy on 20 September 1941. On 3 April 1943 U-124 was sunk west of Oporto with the loss of all 53 crew by depth charges from the corvette HMS Stonecrop and sloop HMS Black Swan.
U-201 was a type VIIC ocean-going submarine built by Germania shipyard, Kiel. Launched 7 December 1940 and commissioned 25 January 1941. Another U-boat with an outstandingly successful record, at the time of the action against HG 73 she was commanded by Kapitänleutnant Adalbert Schnee, and had been summoned to assist U-124 on the attack on OG 74 but was driven off by attack from fighters from the escort carrier HMS Audacity. On the night of 21/22 September, however, she caught up with and sank three stragglers from that convoy. U-201 was sunk with all 49 hands on 17 February 1943 east of Newfoundland by depth charges from HMS Viscount, though by this time Schnee was directing operations against the convoys for Admiral Dönitz.
U-203, also a Germaniawerft type VIIC boat, was launched 4 January 1941 and commissioned on 18 February. She was commanded at this time by Kapitänleutnant Rolf Mützelburg, who with Mohr and Schnee earned the Knights Cross with Oak Leaves for his exploits. She was sunk on 25 April 1943 south of Cape Farewell by bombs from aircraft operating from the British escort carrier HMS Biter and depth charges from the destroyer HMS Pathfinder. 10 crew were killed. Mützelburg himself had died in a freak accident a few months earlier.
U-205 was the third Germaniawerft type VIIC boat but not commissioned until 3 May 1941, under the command of Kapitänleutnant Franz-George Reschke. Perhaps an unhappy boat, one of her crew took his own life just a few days later on 30 September, and she sank only two ships during 11 patrols. U-205 was eventually lost on 17 February 1943 in the Mediterranean to depth charges from the destroyer HMS Paladin.
Information about convoy HG 73 and the ships lost is taken mainly from Arnold Hague's 'The Allied Convoy System 1939-1945' (Vanwell Publishing, Ontario, and Chatham Publishing, London, 2000). Details of the attack on the convoy itself have been taken largely from U-boat.net though I have tried to reconcile differences between the sources where possible.
Technical information about the U-boats involved is partly from Gröner, Jung and Maass 'German Warships 1815 -1945 vol. 2' (English language ed. published by Conway Maritime Press, London, 1991) as well as U-boat.net, a highly recommended site.