The 6-inch siege gun model 1877 (Russian: 6-дюймовая осадная пушка образца 1877 года) was a Russian 152.4 mm (6 in) fortress gun, siege gun and coastal defense gun. It was used in the Russo-Japanese War, World War I, and the Russian Civil War. The successor states of the Russian Empire also inherited a number of M1877 guns.