The Lyon class was a set of battleships planned for the French Navy (Marine Nationale) in 1913, with construction scheduled to begin in 1915.

The first two were named for cities in France, and the latter pair honored the French admirals Abraham Duquesne and Anne Hilarion de Tourville.

The French Navy began a dreadnought battleship construction program in 1910 with the four ships of the Courbet class.

The French were aware that the latest British battleships—the Queen Elizabeth class—were to be armed with 38 cm (15 in) guns, prompting significant consideration of matching this caliber for the Lyon design.

[4] The first proposal by the Directorate of Artillery (Direction de l'artillerie) was for the existing 45-caliber[a] gun used by the Bretagne and Normandie-class ships to be modified to use a slightly longer shell that weighed 590 kg (1,300 lb), 50 kg (110 lb) more than the existing shell, and was optimized for underwater performance.

The French government mobilized its reserve forces in July, a month before the conflict, and thereby stripped its shipyards of many of the specialized tradesmen required for constructing the ships.

The final design called for a propulsion system rated at 40,000 metric horsepower (39,000 shp) with a top speed of 21 knots (39 km/h; 24 mph).

[7] A preliminary sketch, attached to the design staff's memo of 19 September 1913, showed one turret was placed forward, one amidships, and two in a superfiring pair aft, although the contemporary Journal of United States Artillery suggests the turrets would have been mounted in two superfiring pairs, forward and aft.

After learning that shells had penetrated the hulls of battleships underwater to burst below their armored belts during the Battle of the Yellow Sea in 1904 and during British gunnery trials in 1907, the French Navy began investigating how they might optimize shell design to improve their performance through the water.

[12] The secondary armament was to consist of twenty-four guns, either the 55-caliber 138.6 mm Modèle 1910 or a new automatic model, each singly-mounted in casemates in the hull sides.

[13] The ships would also have been equipped with a pair of 47 mm (1.9 in) anti-aircraft guns and six submerged torpedo tubes of unknown size.