During World War I she provided cover for the Otranto Barrage that blockaded the Austro-Hungarian Navy in the Adriatic Sea, but saw no action.

The ship was significantly modernised in the interwar period, and when she was on active duty, conducted normal peacetime cruises and training manoeuvres in the Mediterranean and the Atlantic Ocean.

After World War II broke out in September 1939, Bretagne escorted troop convoys and was briefly deployed to the Atlantic in search of German blockade runners and commerce raiders.

They carried enough coal and fuel oil to give them a range of 4,700 nautical miles (8,700 km; 5,400 mi) at a speed of 10 knots (19 km/h; 12 mph).

[3] The Bretagne class's main battery consisted of ten Canon de 34 cm (13.4 in) modèle 1912 guns mounted in five twin-gun turrets, numbered one to five from front to rear.

The secondary armament consisted of twenty-two Canon de 138 mm (5.4 in) modèle 1910 guns mounted individually in casemates along the length of the hull.

[7] Bretagne was laid down on 22 July 1912 at the Brest Arsenal, launched on 21 April 1913, completed on 29 November 1915, and commissioned into the fleet on 10 February 1916.

On 18 July, Bretagne, France and the battleship Paris began a cruise visiting French ports in the Bay of Biscay and English Channel.

Bretagne transported the Navy Minister, Georges Leygues, to Malta for an official visit over the period 27 April – 1 May 1926.

[18] Provence reassumed the role of fleet flagship[14] on 1 October 1927 when Bretagne prepared to begin a refit to overhaul her boilers that began on 15 November and lasted until 12 May 1928.

A pair of 4.57-metre (15 ft) rangefinders were added on the conning tower roof, another one in the DCT at the top of the foremast and another at the base of the mainmast.

[19] On 3 July 1928, Bretagne, Provence and their sister Lorraine participated in a fleet review by the President of France, Gaston Doumergue, at Le Havre and they spent the following year in the Mediterranean.

Bretagne, Provence and Paris participated in another fleet review by Doumergue on 10 May 1930 that commemorated the centennial of the conquest of Algeria.

The ships also made port visits in the islands and French Morocco before sailing to Brest where they arrived on 16 June.

The 2nd Battle Division visited ports in the Azores, Madeira, Portuguese Cape Verde, and French Morocco, returning to Brest on 26 February 1937.

[12] Nonetheless, the sisters escorted troop convoys between France and French North Africa from 1 September to 5 October.

[23] On 4 December, Bretagne and Provence, along with the cruisers Colbert, Dupleix, and Primauguet and several destroyers and submarines operated out of Dakar, French West Africa in search of German commerce raiders and blockade runners without success.

On the return voyage, they escorted two American merchant ships carrying 82 aircraft bought by France and arrived at Toulon on 10 April.

[14][26][27][28] Bretagne and her sisters passed through the Strait of Sicily on 30 April, covered by the French 3rd Cruiser Division on their way to Alexandria.

Admiral François Darlan, Commander-in-Chief of the French Navy, decided that all capital ships should be concentrated in Mers El Kébir, so he instructed them to steam there.

Bretagne and Provence arrived there on 27 May, where they rendezvoused with the Force de Raid, France's most modern ships, in an unsuccessful effort to deter Italy from joining the war.

Prime Minister Winston Churchill therefore ordered Vice-Admiral James Somerville, the commander of Force H, to neutralise the French fleet at Mers-el-Kébir.

On 3 July, Somerville arrived and delivered the ultimatum; the French rejected it, and so the British ships opened fire.

[31] Bretagne, having remained in Mers El Kébir since being stationed there one month earlier, was hit by four 15-inch (381 mm) projectiles from Hood, Resolution, and Valiant (no ship is individually credited).

The Serra Frères company salvaged Bretagne's wreck, breaking up the vessel for scrap beginning in 1952 and completing the job on 21 December 1954.