Neptune and her sister ships suffered from a number of problems, including poor stability, insufficient armor protection, and excessive displacement.

Neptune, completed in 1892, had a relatively short and uneventful career, which she spent in the Mediterranean Squadron conducting training exercises.

New pre-dreadnought battleships began to enter service in the mid-1890s, which displaced the Marceaus to the Reserve Division, where they were used as training ships.

Lighter guns allowed a fourth weapon to be added to the main battery, which were rearranged into a lozenge layout that would be used in most French capital ships built over the following ten years.

The class was to have comprised four vessels, but the first unit, Hoche had to be redesigned with a reduced armament after construction began when it became apparent that the initial design was not feasible on the specified dimensions.

[1][2][3] The design of the Marceau-class ships was revised repeatedly during construction, and by the time they were completed, they were seriously overweight, which submerged much of their belt armor and degraded their stability.

She was fitted with a pair of pole masts equipped with fighting tops that carried some of her light guns and spotted for her main battery.

[5][8][9] The ship was protected with a combination of mild steel and compound armor; her belt was 229 to 457 mm (9 to 18 in) thick and extended for the entire length of the hull.

[5] The contract for Neptune was authorized on 7 October 1880,[10] though work on the ship did not begin until her keel laying on 17 April 1882 at the Arsenal de Brest.

[14] She participated in the fleet maneuvers that year as part of the 3rd Division, in company with her sister Marceau and Dévastation, the latter serving as the divisional flagship.

[16] The following year, the Mediterranean Squadron consisted of Neptune, her two sisters, the two Amiral Baudin-class ships, Courbet, Dévastation, the ironclad Redoutable and the new pre-dreadnought battleship Brennus.

[21] The French fleet was reorganized in 1899, and the three Marceau-class ships were organized as a separate division attached to the Mediterranean Squadron for torpedo and gunnery training purposes.

In the 1890s, the French began rebuilding older ironclads to prolong their useful lives, and modernizations for the three Marceaus were authorized that year.

In November and December that year, she was used in tests with shells fitted with experimental warheads that were filled with Planclastite, a combination of nitrogen peroxide and carbon bisulfide.