The Danton-class ships were ordered as the second tranche of a French naval expansion plan that began in response to the growth of the Imperial German Navy after 1900.
Discussions began in 1905 for an enlarged version of the preceding Liberté-class design.
French analyses of the Russian defeat by the Japanese at the Battle of Tsushima in May 1905 credited the latter's victory to the large number of medium-caliber hits that heavily damaged the superstructures of the Russian ships and started many fires that the crews had difficulty extinguishing.
The superior speed and handling of the Japanese ships was also credited with a role in their victory.

The French decided that the increasing range of naval combat dictated the use of the 240-millimeter (9.4 in) gun in lieu of the 194-millimeter (7.6 in) gun used on the Liberté class as the larger gun had a greater ability to penetrate armor at longer ranges while still having a good rate of fire.
The navy also wanted a faster ship, but this could only be done by reducing armor thicknesses without exceeding the 18,000-metric-ton (18,000-long-ton) limit imposed by the Minister of the Navy, Gaston Thomson, for budgetary reasons.
A preliminary design with the usual triple-expansion steam engines was accepted in March 1906, but various modifications were requested.
One proposal was made to replace the 240-millimeter guns turrets with single 305-millimeter (12 in) turrets to create an "all-big-gun" ship, like the British battleship HMS Dreadnought, but this was rejected as it would have raised the displacement above the 18,000-metric ton limit and the slower-firing 305-millimeter guns would have reduced the volume and weight of fire to an unacceptable degree.

Initial parliamentary discussion of the design focused less on the anticipated cost of the ships than the idea that France was being left behind in the technological arms race, particularly in regard to the innovative Parsons steam turbines used by HMS Dreadnought.
In response the navy sent a technical mission to inspect the Parsons factory, several shipyards, and gun factories as well as the Barr & Stroud rangefinder factory in May 1906 and concluded that the turbines offered more power in a smaller volume than triple-expansion steam engines at a significant increase in fuel consumption at low speeds.
Two ships had already been ordered from the naval dockyards three months previously when the navy decided to use the turbines in July.
To further complicate things, Gaston requested a study using the heavier and more powerful 45-caliber 305-millimeter Modèle 1906 gun on 3 August while not endorsing the navy's decision to use turbines.
On 6 October the director of naval construction, M. Dudebout, urgently requested a decision while recommending that three ships use steam engines and the others turbines.
He felt that this would minimize delays and expense as the design needed to be modified to accommodate the turbines and their four propeller shafts, no company in France knew how to build the turbines, and the latter were three times as expensive as steam engines.
Gaston was inclined to accept Dudebout's recommendation, but prevaricated until December, after parliamentary debates showed overwhelming support for turbines in all six ships.
Contracts for the remaining four ships were signed on 26 December, the day after the conclusion of the debate.
Gaston also delayed in deciding on which boilers to use.
He sent another technical mission to Britain to look at Babcock & Wilcox's design in April 1907, but did not make a decision in favor of French-built boilers until 3 June 1908, after all the ships had been laid down.

The design was estimated to displace 18,318 tonnes (18,029 long tons) before the adoption of the heavier Modèle 1906 gun required a new and larger turret to handle the gun which meant that the turret's supporting structure also had to be reinforced.
In an unsuccessful bid to reduce the displacement, many sections of armor were reduced in thickness, but the ships exceeded even the design estimate as built.
The Danton-class ships were ordered as the second tranche of a French naval expansion plan that began in response to the growth of the Imperial German Navy after 1900. Discussions began in 1905 for an enlarged version of the preceding Liberté-class design. French analyses of the Russian defeat by the Japanese at the Battle of Tsushima in May 1905 credited the latter's victory to the large number of medium-caliber hits that heavily damaged the superstructures of the Russian ships and started many fires that the crews had difficulty extinguishing. The superior speed and handling of the Japanese ships was also credited with a role in their victory.
The French decided that the increasing range of naval combat dictated the use of the 240-millimeter (9.4 in) gun in lieu of the 194-millimeter (7.6 in) gun used on the Liberté class as the larger gun had a greater ability to penetrate armor at longer ranges while still having a good rate of fire. The navy also wanted a faster ship, but this could only be done by reducing armor thicknesses without exceeding the 18,000-metric-ton (18,000-long-ton) limit imposed by the Minister of the Navy, Gaston Thomson, for budgetary reasons. A preliminary design with the usual triple-expansion steam engines was accepted in March 1906, but various modifications were requested. One proposal was made to replace the 240-millimeter guns turrets with single 305-millimeter (12 in) turrets to create an "all-big-gun" ship, like the British battleship HMS Dreadnought, but this was rejected as it would have raised the displacement above the 18,000-metric ton limit and the slower-firing 305-millimeter guns would have reduced the volume and weight of fire to an unacceptable degree.
Initial parliamentary discussion of the design focused less on the anticipated cost of the ships than the idea that France was being left behind in the technological arms race, particularly in regard to the innovative Parsons steam turbines used by HMS Dreadnought. In response the navy sent a technical mission to inspect the Parsons factory, several shipyards, and gun factories as well as the Barr & Stroud rangefinder factory in May 1906 and concluded that the turbines offered more power in a smaller volume than triple-expansion steam engines at a significant increase in fuel consumption at low speeds. Two ships had already been ordered from the naval dockyards three months previously when the navy decided to use the turbines in July. To further complicate things, Gaston requested a study using the heavier and more powerful 45-caliber 305-millimeter Modèle 1906 gun on 3 August while not endorsing the navy's decision to use turbines. On 6 October the director of naval construction, M. Dudebout, urgently requested a decision while recommending that three ships use steam engines and the others turbines. He felt that this would minimize delays and expense as the design needed to be modified to accommodate the turbines and their four propeller shafts, no company in France knew how to build the turbines, and the latter were three times as expensive as steam engines. Gaston was inclined to accept Dudebout's recommendation, but prevaricated until December, after parliamentary debates showed overwhelming support for turbines in all six ships. Contracts for the remaining four ships were signed on 26 December, the day after the conclusion of the debate. Gaston also delayed in deciding on which boilers to use. He sent another technical mission to Britain to look at Babcock & Wilcox's design in April 1907, but did not make a decision in favor of French-built boilers until 3 June 1908, after all the ships had been laid down.
The design was estimated to displace 18,318 tonnes (18,029 long tons) before the adoption of the heavier Modèle 1906 gun required a new and larger turret to handle the gun which meant that the turret's supporting structure also had to be reinforced. In an unsuccessful bid to reduce the displacement, many sections of armor were reduced in thickness, but the ships exceeded even the design estimate as built.
Danton-class battleship