240 mm Trench Mortar The 240 mm Trench Mortar , or Mortier de 240 mm , was a large calibre mortar of World War I . An original French design , it was developed by Batignolles Company of Paris and introduced in 1915 . Service . The weapon was dismantled for transport , requiring four carts for the barrel , base , carriage and ammunition . In action , a heavy timber platform was constructed embedded in the ground , on which the mortar base was immovably secured . The mortar carriage sat on the base and could traverse . The mortar barrel and breech were mounted on the carriage which provided elevation . They were used in the " siege warfare " on the Western Front to destroy enemy strongpoints , bunkers and similar " hard " targets which were invulnerable to lighter mortars and field guns . The US Army handbook described it : " . . . the use for which it is primarily adapted is in the bombardment of strongly protected targets — dwellings , covered shelters , command posts , entrances to galleries , etc — or in the destruction of sectors of trenches , salients and the like . " . Their effectiveness decreased late in the war as German policy changed to a lightly held frontline , hence decreasing available targets , and they became redundant when the war of movement resumed in mid - 1918 . 240 mm mortar in French use . The mortar was first introduced in 1915 as the " Mortier de 240 mm CT " ( " court de tranchee " ) . It was a short barreled version which fired a 192 lb ( 87 kg ) bomb for 1 , 125 yards ( 1 , 030 m ) , using a propellant charge of 1 lb 9 oz ( 710 g ) . Its first major use was in the Champagne offensive of September 25 , 1915 . This was followed later by the " Mortier de 240 mm LT " ( " long de tranchée " ) which was a long barreled version with improved firing arrangement and breech - loaded charge which fired a bomb , using a propellant charge of . This appears to be the bomb configuration adopted by USA . French estimates were 80 bombs needed to destroy a strong shelter with a roof of concrete or rails and concrete . 240 mm mortar in US use . David Lupton ' s Sons Co manufactured the weapon in the United States during World War I . The US version appears to have been a direct copy of the Mortier de 240 mm LT , i . e . with longer barrel and propellant charge loaded into the breech via a brass cartridge case , was also produced late in the war but it is doubtful whether any were actually used in combat . The December 1917 manual describes the weapon as " 9 . 45 inch " but makes clear it is the French 240 mm they are describing that the US has adopted . The bomb is described as weighing , with an explosive charge of and range from 660 to . The March 1918 manual describes the Bomb , Model 1916 , Type T , weight , explosive , length 1 . 02 m ( 40 in ) . Barrel and breech weighing , carriage , base , timber platform . Propellant charges of 800 grams Ballistite + 15 grams F - 3 black powder for 750 – 1400 meters , and 1250 grams Ballistite + 15 grams F - 3 for 1100 – 2200 meters . This figure agrees with the charge quoted for the mortar in French use for maximum range . " Separate loading ammunition " was used i . e . the mortar bomb was a separate unit from the propellant cartridge case , which was flanged , brass , 9 . 776 inches long x diameter ( 248 . 3 by 169 . 4 mm ) . The bomb was loaded into the barrel muzzle . The cartridge containing propellant charge appropriate for the required range was loaded into the breech , similar to a howitzer . The mortar was fired by pulling a lanyard , which triggered a primer in the base of the cartridge case and ignited the propellant charge in the cartridge . The cartridge cases could be reused after cleaning and replacing the primer . 240 mm Mortar in Italian Use . Italy used both the French CT and LT versions and produced their own long barrel version . Austro - Hungarian 24 cm Minenwerfer M . 16 . Some 400 were copied and manufactured by Böhler during World War I based on examples captured from Italy , although the Austrians had problems recreating the original powder mixture and their shells suffered from large dispersions . German 24 cm s . Flügelminenwerfer . The US A . E . F . in France reported in March 1918 : " . . . a new pattern minenwerfer which was brought out in 1916 and looks very much like the French 240 . . . uses a heavy bomb fitted with four vanes like the French 240 mm bombs . This bomb weighs 100 kg ( 220 lb ) and contains 42 kg ( 93 lb ) of explosive . . . ranges obtained vary from 490 to 1310 yards " . The specifications appear similar to the early French 240 mm CT quoted above . It is unknown whether this was related to the French or Austrian Böhler versions . The US manuals for the mortar appear to be based on French manuals e . g . the soldiers depicted are in French uniform .