Neptune was an ironclad of the French Navy built in the 1880s and early 1890s. She was the second member of the Marceau class, which included two other vessels. The Marceau class was based on the earlier Amiral Baudin class of barbette ships, but with smaller guns: four 340 mm (13.4 in) weapons compared to the three 420 mm (16.5 in) guns of the earlier vessels. They introduced the lozenge arrangement for their main battery that became common for many French capital ships built in the 1890s. Neptune and her sister ships suffered from a number of problems, including poor stability, insufficient armor protection, and excessive displacement.