On her third patrol, she missed the German U-boat U-23 and was damaged after hitting the bottom, requiring repairs.

Sturgeon was transferred to the 8th Submarine Flotilla, which operated on the Mediterranean Sea, in October 1942 to support the Allied landings in North Africa.

The S-class submarines were designed as successors to the L class and were intended to operate in the North and Baltic Seas.

[3] For surface running, the boats were powered by two 775-brake-horsepower (578 kW) diesel engines, each driving one propeller shaft.

[5] On 23 August, Sturgeon departed her homeport of Portland along with her sister ships Spearfish and Swordfish.

When Britain declared war against Nazi Germany on 1 September, this became Sturgeon's first combat patrol.

On 4 September 1939, Sturgeon, on her way to return to Dundee, was erroneously bomber by a British aircraft at 16:20 (UTC) in position 56°34′N 01°04′W / 56.567°N 1.067°W / 56.567; -1.067.

On 14 September, Sturgeon sighted an unidentified submarine, thought to be a German U-boat, and fired three torpedoes at it in position 56°22′N 01°28′W / 56.367°N 1.467°W / 56.367; -1.467, south-east of Aberdeen, Scotland.

Two days later on 16 October, Sturgeon hit the bottom at 60 feet (18 m) depth, damaging her ASDIC dome.

On 20 November, she sank the German armed trawler V 209 Gauleiter Telshow with torpedoes approximately 50 nautical miles (93 km; 58 mi) northwest of Heligoland in position 54°34′N 06°28′E / 54.567°N 6.467°E / 54.567; 6.467.

[6] After an uneventful seventh war patrol in the North Sea, Sturgeon underwent a refit at Wallsend until 14 April 1940.

After shifting back to Blyth, she conducted an uneventful eighth patrol southwest of Stavanger, Norway from 30 April to 11 May 1940.

On 9 June, she was ordered to patrol close to the British east coast because of fears that German warships would conduct a raid there.

On 4 August, she sighted the German patrol boat V-811, which was being towed by a tug after hitting a mine.

On 2 September, she torpedoed and sank the German troop transport Pionier 15 nautical miles (28 km; 17 mi) north of Skagen, Denmark in position 57°56′N 10°46′E / 57.933°N 10.767°E / 57.933; 10.767.

The next day, Sturgeon attempted to attack the Norwegian vessel Ulv at 58°41′N 09°21′E / 58.683°N 9.350°E / 58.683; 9.350, but both torpedoes missed their target.

[6] From 28 November 1940 23 February 1941, Sturgeon conducted three uneventful patrols off Bergen, Stadlandet, and Lista, Norway.

[6] After repairs, Sturgeon departed Portsmouth on 26 July 1941 for another patrol in the Bay of Biscay, her twenty-third since the beginning of the war.

[6] On 24 April 1942, Sturgeon departed Holy Loch for another patrol mission, in the Norwegian Sea, as an escort of Convoy PQ 15.

[6] After repairs at Chatham Dockyard and Scapa Flow, Sturgeon sailed for Gibraltar on 27 October 1942, temporarily assigned to the 8th Submarine Flotilla which operated in the Mediterranean Sea.

On 6 November, Sturgeon was mistakenly attacked by Lockheed Hudson aircraft, which dropped three depth charges in position 36°02′N 06°33′W / 36.033°N 6.550°W / 36.033; -6.550, causing no damage.

[6] On 10 November 1942, Sturgeon departed Gibraltar for her thirtieth (first in the Mediterranean) patrol, off Toulon, France, then Naples, Italy.

On 13 May, she shifted to Plymouth for a refit, but before it could be completed, she was loaned to the Royal Netherlands Navy, which renamed her RnMs Zeehond.

[6][8] Under the command of Donald Theodoor Mackay, Zeehond shifted to Portsmouth, then departed for the River Clyde on 11 November 1943.

However, she encountered heavy seas and used too much fuel for the trip, forcing her to return to Londonderry, Northern Ireland.

After sailing through various British port cities, Zeehond departed Lerwick on 18 March for her second war patrol, off the Norwegian coast.