Canon de 27cm Mle 1870
Used in battleships and coast defenses c.1870~1918.
274mm caliber 216kg shells, 434m/s muzzle velocity giving it an estimated 300mm of penetration in wrought iron armor at combat range, breech-loading single shot.
Picture taken c.1885 by Gustave Bourgain onboard a Colbert-class French ironclad, below the center battery.
Note the boarding weapons on racks on the left side of the picture, including cutlasses and Lefaucheux Mle1858 revolvers. The Colbert-class ironclads were also armed with, beside a variety of other naval guns, more than a dozen Hotchkiss 37mm revolving cannons, four 356mm torpedo tubes and a ram.