Léon Gambetta was the lead ship of her class of three armored cruisers built for the French Navy (Marine Nationale) in the first decade of the 20th century.

[2] The main battery of the Léon Gambetta class consisted of four 194-millimeter Modèle 1893–1896 guns mounted in twin-gun turrets fore and aft of the superstructure.

The cruiser ran aground in fog while conducting trials in late February 1904; two of her propellers and a large amount of hull plating had to be replaced.

After resuming her trials in August, the cruiser briefly went aground again while trying to navigate the narrow entrance to the River Penfeld in early September.

Léon Gambetta participated in the Northern Squadron's visit to Portsmouth the following month to commemorate the signing of the Entente Cordiale allying France and Britain.

Vice Admiral Horace Jauréguiberry had assumed command of the squadron by October when she ferried Émile Loubet, President of France, home from a state visit in Lisbon, Portugal.

In May 1908 The ship transported Armand Fallières, who succeeded Loubet as President, to Dover, England, and in July participated in the Quebec Tercentenary in Canada.

By 4 April 1911, the 1st DL consisted of all three sisters with Léon Gambetta serving as the flagship of Rear Admiral (Contre-amiral) Louis Dartige du Fournet.

On 13 August Vice Admiral Augustin Boué de Lapeyrère, commander of the Allied forces in the Central Mediterranean, was ordered to begin offensive operations against the Austro-Hungarian fleet in the Adriatic.

The 2nd DL escorted the cargo ship SS Henri Fraissinet as it brought long-range artillery pieces to Antivari on 18–19 September.

During the following mission, begun at the end of October, the 2nd DL raided the island of Lastovo on 2 November and Jules Ferry was narrowly missed by U-5, an Austro-Hungarian U-boat, on the return voyage the following day.

Boué de Lapeyrère, concerned about a possible pre-emptive attack on the southern Italian ports, temporarily moved all of his armored cruisers closer to the Strait of Otranto that day.

Unbeknownst to Léon Gambetta, she had been stalked for a day and a half by Korvettenkapitän (Lieutenant Commander) Georg Ritter von Trapp, the new commander of U-5, when the submarine was finally able to make her attack at 00:40 on 27 April, roughly 15 nautical miles (28 km; 17 mi) south of Santa Maria di Leuca (the south-eastern tip of Italy in the Ionian Sea).

One of the lifeboats subsequently sank due to overcrowding; only 137 men out of her crew of 821 were rescued by the Italian destroyers Impavido and Indomito and two torpedo boats.

[13] After the sinking, Boué de Lapeyrère withdrew his armored cruisers even further south to a patrol line running through the Gerogombos lighthouse on the island of Cephalonia.