French submarine Achéron

At the start of World War II in September 1939, Achéron was assigned to the 3rd Submarine Division in the 2nd Squadron — a component of the 1st Flotilla — based at Toulon, France.[3] Her sister ships Actéon, Fresnel, and Protée made up the rest of the division.[3][4] In December 1939, Achéron joined Fresnel and their sister ships Le Héros and Redoutable in searching the central Atlantic Ocean for the German supply ship Altmark.[3][5] Agosta and Béveziers, which were returning to France from the French West Indies, also joined in the search.[3]

At the beginning of February 1940, the 3rd Submarine Division transferred briefly to Casablanca in French Morocco and on 6 February 1940 began patrols off the Canary Islands, where the Allies believed that German cargo ships[3] had taken refuge at the beginning of the war and were serving as supply ships for German U-boats. During these patrols, Achéron opened fire with her deck gun on a 5,265-gross register ton steam cargo ship that her crew suspected of being a German blockade runner, forcing the ship to stop in the Atlantic Ocean at 34°25′N 018°08′W.[3] Crewmen from Achéron boarded the ship and determined that she was the British merchant ship SS Somme,[3] after which Achéron allowed her to proceed.

On 12 April 1940, the 3rd Submarine Division was transferred to the Mediterranean Sea, based first at Bizerte in Tunisia. While Fresnel remained at Bizerte, the division′s other submarines then transferred to Beirut in the French Mandate for Syria and Lebanon, from which they operated under the command of the British Commander-in-Chief, Mediterranean Fleet, Admiral Andrew Cunningham at Alexandria, Egypt.[3][6] Achéron patrolled in the Eastern Mediterranean in the approaches to Beirut.

German ground forces advanced into France on 10 May 1940, beginning the Battle of France, and Italy declared war on France on 10 June 1940 and joined the invasion. On the day Italy entered the war, British submarines based at Beirut departed for operations in the Aegean Sea off the Dardanelles and in the Tobruk area off the coast of Libya, and on 11 June the French submarines L'Espadon, Phoque, and Protée also departed to operate in the Dodecanese, leaving only Achéron to defend the approaches to Beirut.[3] On 16 June 1940, an Italian torpedo boat fired a torpedo at Achéron, but missed.[3]

The Battle of France ended in France's defeat and an armistice with Germany and Italy, which went into effect on 25 June 1940. Achéron — by then assigned to the 3rd Submarine Division in the 3rd Squadron in the 1st Flotilla[3] — was recalled to Beirut.[7]

After France's surrender, served in the naval forces of Vichy France. Her batteries and those of her sister ship Actéon — which also was at Beirut — were in poor condition, but repairing or replacing them was impossible at Beirut.[8] Escorted by the netlayer Le Gladiateur, the two submarines departed Beirut on 16 October 1940 bound for Toulon, which they reached on 24 October 1940.[3][8] At Toulon, Achéron was placed under guard and maintained in a disarmed and unfueled state in accordance with the terms of the Armistice of 22 June 1940.[9] By 1 November 1942, still in this status at Toulon, Achéron had been assigned to the 1st Submarine Group along with her sister ships L'Espoir, Le Glorieux, and Vengeur.[3]

Achéron was at Toulon when Germany and Italy occupied the Free Zone (French: Zone libre) of Vichy France on 27 November 1942, and she was among the French vessels scuttled at Toulon to prevent their seizure by Germany when German forces entered the naval base that day,[2][10] sinking in Dock No. 3 of the Vauban Grand Docks.[3]

The Germans seized Achéron and handed her over to the Italians for scrapping.[3] Her wreck lay in a position where her stern hindered the closing of Dock No. 3, so divers cut her stern.[3][11] The Italians refloated her on 26 June 1943,[2][3] but she was still at Toulon when Italy surrendered to the Allies on 9 September 1943. The Germans seized her and earmarked her for scrapping, but 88 American bombers dropped 240 short tons (210 long tons; 220 tonnes) of bombs on the Toulon Arsenal and sank her on 24 November 1943 before she could be scrapped.[2][12]

• Fontenoy, Paul E. (2007). Submarines: An Illustrated History of Their Impact (Weapons and Warfare). Santa Barbara, California. ISBN 978-1-85367-623-9.{{cite book}}: CS1 maint: location missing publisher (link)
• Gardiner, Robert; Chesneau, Roger (1980). Conway's All the World's Fighting Ships 1922–1946. London: Conway Maritime Press. ISBN 0-85177-146-7.
• Huan, Claude (2004). Les Sous-marins français 1918–1945 (in French). Rennes: Marines Éditions. ISBN 9782915379075.
• Picard, Claude (2006). Les Sous-marins de 1 500 tonnes (in French). Rennes: Marines Éditions. ISBN 2-915379-55-6.