French submarine Diane (NN4)

Diane was a French Navy Diane-class submarine commissioned in 1932, the lead ship of her class. During World War II, she operated on the Allied side until 1940, when she became part of the naval forces of Vichy France. She was scuttled in November 1942.

Construction and commissioning
Ordered in 1926 under Naval Program 75, Diane was laid down at Chantiers et Ateliers Augustin Normand in Le Havre, France, on 25 April 1927. She was launched on 13 May 1930. After fitting out, she was commissioned for trials on 15 July 1930. Her official trials began on 2 January 1931, and her final equipping and armament took place at Cherbourg, France, from 1 April 1931 to 30 January 1932. She was placed in full commission on 1 September 1932.

Pre-World War II
During a visit to Bénodet, France, Diane lost a member of her crew on 25 May 1937 who drowned while attempting to swim about 300 m from shore to Diane. The incident occurred after he and three other crewmen had returned to shore when the boat they tried to use to reach Diane began to fill with water, and three of the men decided to swim to Diane.

French Navy
When World War II began on 1 September 1939 with the German invasion of Poland, Diane was part of the 14th Submarine Division — a part of the 2nd Submarine Squadron in the 6th Squadron — along with the submarines FRENCH SUBMARINE Ariane, FRENCH SUBMARINE Danaé, and FRENCH SUBMARINE Eurydice, based at Oran in Algeria. France entered the war on the side of the Allies on 3 September 1939. Diane subsequently patrolled in the Atlantic Ocean in the vicinity of Madeira.

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. The Battle of France ended in France's defeat and an armistice with Germany and Italy on 22 June 1940. When the armistice when into effect on 25 June 1940, Diane still was based at Oran.

Vichy France
After France′s surrender, Diane served in the naval forces of Vichy France. On 3 July 1940, the British began Operation Catapult, which sought to seize or neutralize the ships of the French Navy to prevent their use by the Germans, and Diane was in port at the French naval base at Mers El Kébir at Oran that day when a British naval squadron arrived off the base and demanded that the French Navy either turn over the ships based there to British custody or disable them. The French put their submarines at Oran on alert, and at 13:30 Diane and Eurydice were ready for sea They anchored in the outer harbor at 15:00 or 15:30 (sources disagree) with Ariane and Danaé, and at 17:54 the four submarines received orders to put to sea.

When the British warships opened fire on the French ships in the harbor at 17:57, beginning their attack on Mers-el-Kébir, Diane was 3.5 nmi west of Pointe de l’Aiguille (35.87528°N, -0.48444°W) in Oran Province. None of the four submarines was able to close with the British ships during the battle. During the night of 3–4 July 1940, the four submarines patrolled on the surface off Oran in a north-south patrol line. All four submarines remained on patrol off Oran until 20:00 on 4 July 1940 before returning to Oran.

As Operation Catapult continued, British forces attacked the French squadron at Dakar in Senegal on 8 July 1940. Receiving word of the attack, French naval authorities at Oran ordered Eurydice, Ariane, and Diane to form a patrol line off Cape Falcon, Algeria.

Diane spent August and September 1940 at Toulon, France, then returned to Oran. From October 1941 to May 1942, she was under guard at Oran in an unarmed and unfueled status in accordance with the terms of the 22 June 1940 armistice. By 1 November 1942, still in that status, she was part of the 12th Submarine Division.

Loss
Diane still was in her unarmed and unfueled status at Oran when Allied forces invaded French North Africa in Operation Torch on 8 November 1942. She was scuttled at Oran on 9 November 1942 to prevent her capture by Allied forces. Her wreck was condemned in 1944.