The 21 cm Haubitze M1891 or (21 cm Howitzer Model 1891) in English was a fortress gun built by Krupp that armed the forts of several European countries before World War I. Two countries that bought the M1891 were Belgium and Romania. In Belgian service it was designated Obusier de 21c.A. and in Romanian service it was designated Obuzierul Krupp, calibrul 210 mm, model 1891.