sentences:  It was nicknamed the "Goon Gun" (from its large bullet-shaped shells, monopod, and rifled bore – like a rifle for shooting Goons) or the "Four-Deuce" (from its bore size in inches).In 1951 it began to be phased out in favor of the M30 mortar of the same caliber.The first 4.2-inch mortar in U.S. service was introduced in 1928 and was designated the M1 Chemical Mortar.