French battleship Vergniaud

During the war 75 mm anti-aircraft guns were installed on the roofs of the ship's two forward 240 mm gun turrets.[3] During 1918, the mainmast was shortened to allow the ship to fly a captive kite balloon and the elevation of the 240 mm guns was increased which extended their range to 18,000 meters (20,000 yd).[1]

At the beginning of the war, the ship, together with her sister Condorcet and the dreadnought Courbet, unsuccessfully searched for the German battlecruiser Goeben and the light cruiser Breslau in the Balearic Islands. She later escorted troop convoys from North Africa to France before she joined her sisters[6] at Malta. On 16 August 1914 the combined Anglo-French Fleet under Admiral Auguste Boué de Lapeyrère, including Vergniaud, made a sweep of the Adriatic Sea. The Allied ships encountered the Austro-Hungarian cruiser SMS Zenta, escorted by the destroyer SMS Ulan, blockading the coast of Montenegro. There were too many ships for Zenta to escape, so she remained behind to allow Ulan to get away and was sunk by gunfire during the Battle of Antivari off the coast of Bar, Montenegro. Vergniaud was one of the ships that bombarded Cattaro on 1 September and blockaded the Strait of Otranto for the rest of the year and through August 1915. She was based at Malta and Bizerte until February 1916 when she sailed to Toulon.[3]

Vergniaud was transferred to the Second Squadron on 27 March 1916 and resumed her former duties of blockading the Strait of Otranto from bases in Argostoli and Corfu for most of the rest of the war.[3][5] The ship transferred some of her men to her sister Mirabeau that participated in the Allied attempt to ensure Greek acquiescence to Allied operations in Macedonia in Athens on 1 December 1916. The lieutenant in charge of her landing party was killed as were several other men during the incident.[3] She was given a short refit at Toulon from 9 November 1917 to January 1918 and returned to Corfu. Vergniaud was transferred to Mudros in May to prevent Goeben from breaking out into the Mediterranean. A boiler burst on 14 September, killing four men and wounding nine others. After the Armistice of Mudros was signed on 30 October between the Allies and the Ottoman Empire, the ship participated in the early stage of the occupation of Constantinople. She returned to Toulon on 17 December for a short refit.[7]

In early 1919, Vergniaud was among the ships stationed off Sevastopol as an Allied deterrent to Soviet forces who were encroaching on the city during the Russian civil war. Despite Allied support, the city's White Russian forces were in a seemingly hopeless position, and in April 1919 the French naval high command ordered the ships to evacuate. Rejecting this, the commander of the Second Squadron, Vice-Admiral (vice-amiral) Jean-Françoise-Charles Amet, attempted to have his forces intervene in the fighting, only to have a mutiny erupt on several of his ships. War-weary sailors demanded to return home and the ensuing standoff culminated in a mass shooting of sailor demonstrators. Fifteen people were wounded, but only one died, a sailor from Vergniaud. The battleship's crew had thus far remained neutral in the conflict but quickly joined the ranks of the most radical mutineers, unfurling red banners in support of the Bolshevik forces. The four-day stalemate ended in a victory for the sailors: the ships withdrew from the Black Sea and Vergniaud returned to France.[8] The ship departed on 29 April, towing the merchant ship SS Jerusalem to Constantinople.[7]

A surviving pair of 240mm/50 Modèle 1902 guns from the Vergniaud that were mounted on the Île de Gorée in Senegal.

Vergniaud was based in Beirut from May to August 1919 to monitor Turkish activities off the coasts of Palestine, Lebanon and Syria. She arrived in Toulon on 6 September and was placed in special reserve on 1 October. This ship was later found to be in poor shape, decommissioned in June 1921 and condemned on 27 October. She was disarmed in 1922. Nine of her 240mm guns were installed as coastal defence batteries around the port city of Dakar, Senegal.[9] Two of the guns and their barbettes were sited on the Île de Gorée; due to their prominence they have become known as the "Les canons de Navaronne" after the eponymous 1961 film The Guns of Navarone.[10] In 1940, the port batteries forced an Allied fleet to withdraw from the Vichy French port during the Battle of Dakar.[11]

Vergniaud became a target ship and was used to evaluate the effects of poison gases and bombs until 1926. She was listed for disposal on 5 May 1927 and was sold for breaking up on 27 November 1928 for the price of 5,623,123 francs.[7] A monument to the French mutineers of 1919 was erected by the Soviets in Sevastopol, at Morskaïa Square where Vergniaud's sailor was killed.[8]