French submarine Thétis

In 1937, Thétis sank the decommissioned armored cruiser Jules Michelet as a target.[5]

When World War II began with Nazi Germany′s invasion of Poland on 1 September 1939, Thétis was part of the 13th Submarine Division of the 5th Submarine Squadron in the 1st Flotilla of the 2nd Squadron along with her sister ships Calypso, Circé, and Doris at Toulon.[3] France entered the war on 3 September 1939.

In 1940, the Allies made plans to intervene in Norway to prevent the shipment of iron ore from Sweden to Germany via Narvik on the Norwegian coast. Twelve French submarines were to participate in the operation, including the four submarines of the 13th Division, under the overall command of Royal Navy Vice Admiral Max Horton. Accordingly, Thétis and Calypso got underway from Bizerte, Tunisia, on 23 March 1940 and proceeded to Harwich, England, where the French Navy submarine tender Jules Verne was to support them as they patrolled the Heligoland Bight and the southern North Sea in support of the Norway operation.[3]

The Allies′ plans for Norway took on greater urgency on 9 April 1940, when Germany began Operation Weserübung, its invasion of Norway and Denmark. Circé arrived at Harwich on 14 April and Doris on 20 April to join Calypso and Thétis in supporting Allied operations in Norway. The French submarines found limited facilities available to them at Harwich and had to rely largely on Jules Verne and spare parts sent from Cherbourg in France for repairs, some of which never were completed.[3]

By 6 May 1940, the Allies had indications that a German invasion of the Netherlands was imminent, and that day Horton ordered all available submarines to put to sea. Four French submarines, including Thétis, received orders to join four British and two Polish submarines in forming a patrol line off the coast of the Netherlands to find and attack German submarines believed to be operating in the area. The Battle of France began when German ground forces advanced into France, the Netherlands, Belgium, and Luxembourg on 10 May 1940.[3]

On 4 June 1940, Jules Verne and all the French submarines assigned to her at Harwich departed Harwich and proceeded to Brest, France.[3][6] Italy declared war on France on 10 June 1940 and joined the invasion of France that day. As German ground forces approached Brest on 18 June 1940, all French ships received orders at 18:00 to evacuate the port, with those unable to get underway ordered to scuttle themselves. At 18:30, Jules Verne and 13 submarines, including Thétis, got underway from Brest bound for Casablanca, French Morocco, which they reached on 23 June 1940.[3][6]

The Battle of France ended in France's defeat and armistice with Germany and Italy, which went into effect on 25 June 1940. On that day, Thétis, Calypso, and Circé were still part of the 13th Submarine Division, based at Toulon but assigned to overseas duty at Casablanca.[3]

After the armistice went into effect, Thétis served in the naval forces of Vichy France. By 1 November 1942, she was at Toulon, under guard in an unarmed and unfueled status in accordance with the terms of the 1940 armistice.[3]

On 8 November 1942, Allied forces landed in French North Africa in Operation Torch. On 9 November, the Armistice Commission authorized the reactivation of Vichy French vessels at Toulon, including Thétis, to defend Toulon against any Allied attack there. Thétis was not yet able get underway 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 Toulon that day.[2][3]

• Conway : Conway's All the World's Fighting Ships 1922–1946 (1980) ISBN 978-0-85177-146-5
• Gardiner, Robert; Gray, Randal, eds. (1985). Conway's All the World's Fighting Ships 1906–1921. Annapolis: Naval Institute Press. ISBN 0-87021-907-3.
• Moulin, Jean (2006). Les sous-marins français (in French). Rennes: Marines Éditions. ISBN 2-915379-40-8., pp. 22–23.