The largest mortars ever developed were the French `` Monster Mortar '' ( 36 French inches ; 975 mm ; developed by Henri-Joseph Paixhans in 1832 ) , Mallet 's Mortar ( 36 inches ; 910 mm ; designed by Robert Mallet and tested by the Woolwich Arsenal , London , in 1857 ) and the `` Little David '' ( 36 inches ; 914.4 mm ; developed in the United States for use in World War II ) .
The biggest mortars ever made were the French `` Monster Mortar '' ( 36 French inches ; 975 mm ; developed by Henri-Joseph Paixhans in 1832 ) , Mallet 's Mortar ( 36 inches ; 910 mm ; designed by Robert Mallet and tested by the Woolwich Arsenal , London , in 1857 ) and the `` Little David '' ( 36 inches ; 914.4 mm ; developed in the United States for use in World War II ) .