St. Chamond arsenal was in charge of the transformation, and for this reason, nine 340mm Modèle 1887 L/42 naval guns were obtained, three from the Brennus decommissioned battleship, and six from two retired Valmy class coastal ships. After recalibrating them, these howitzers were designated as “Obusier de 400 Modèle 1915”. Six howitzers were delivered in 1915 and three in 1916, although one howitzer would be left to carry out tests. In 1917 a second order of four other howitzers plus three spare barrels was again entrusted to St. Chamond firm and on this occasion the naval guns chosen were the 340mm Modèle 1912 L/45 arrived after the cancellation of the Normandie class battleships. After modifications, these howitzers were designated as “Obusier of 400 Modèle 1916”. The USA used two Mle 15-16 during the WWI, here we see it in action with gunners from that country in 1918.Each French battery consisted of two howitzers and about 125 men for its handling. The battery was transported in two trains, the “firing train” consisting of a locomotive, two ammunition carriages, a workshop wagon and one or two railway guns and the so-called “administrative train” composed by a locomotive, a headquarters wagon, a kitchen wagon , additional ammunition carriages, three or more berthing carriages and several carriages with lifting equipment and diverse material. These howitzers participated in The Somme and Verdun battles.
