The process of manufacture of recuperators requires four steps--forging, rough machining, finish machining, and assembling. In the case of 155-millimeter howitzer recuperators all the machining was done by one firm; in the other cases rough machining was done by various firms, including, in the case of the 155-millimeter gun and 240-millimeter howitzer recuperators, the firms doing the forging. Complete records of rough machining are not available. In discussing here, therefore, the production of field artillery in the war period, we are concerned chiefly with carriages and recuperators, for they offered the major difficulties. Since the production of gun bodies for these various units has been taken up in the preceding chapter, such reference to them as is necessary will be brief. For the sake of additional clearness in the mind of the reader inexpert in these things, the line should be sharply drawn between field artillery and the so-called railway artillery, which was also mobile to a limited degree. The mobile field artillery consisted of all rolling guns or caterpillar guns up to and including the 240-millimeter howitzer in size; and also included the antiaircraft guns of various sizes. All mobile guns of larger caliber than the 240-millimeter howitzer were mounted on railroad cars. The list of the mobile field artillery weapons in manufacture here during the war period was as follows: The little 37-millimeter gun, the so-called infantry cannon, one of which two husky men could lift from the ground--a French design; The 75-millimeter guns--three types of them--the French 75, adopted bodily by the United States; our own 3-inch gun redesigned to the French caliber; and the British 3.3-inch gun, similarly redesigned; The 4.7-inch gun of American design; The 5-inch and 6-inch guns, taken from our coast defenses and naval stores and placed on mobile mounts; The 155-millimeter gun, a French weapon with a barrel diameter of approximately 6 inches; The 155-millimeter howitzer, also French; The 8-inch and 9.2-inch howitzers, British designs, being manufactured in the United States when war was declared; The 240-millimeter howitzer, French and American; and, finally, The antiaircraft guns. In modern times, but prior to 1917, the United States had designed types of field-artillery weapons and produced them in quantities shown by the following tabulation: Pieces. 2.95-inch mountain gun 113 3-inch gun 544 4.7-inch gun 60 5-inch gun 70 6-inch howitzer 40 7-inch howitzer 70 --- Total 897