42-line fortress and siege gun Pattern of 1877

42 line gun M1877 (42-линейная пушка образца 1877 года) was a siege gun used by the Russian Imperial Army in late 19th and early 20th centuries. The word "line" in the designation refers to a measurement unit which equals 0.1 inch. Curiously, the "model year" was not the year when the weapon was designed or standardized, but the year when a new rifling system was adopted.

The gun was initially developed by the German arms manufacturer Krupp and was based on an earlier 105 mm piece. The 105 mm weapon was demonstrated to a group of Russian Army officers along with a 120 mm design. The delegation liked the 105 mm weapon, but wanted Krupp to change the caliber to a traditional Russian caliber of "42 lines" (106.7 mm). Later the weapon entered production in Russia; it remained in production until 1903.

It should not be confused with the 42 Line battery gun Model of 1877, a field gun version which had a shorter barrel and lower muzzle velocity.