The first of these recuperators to come into quantity production was that for the 155-millimeter howitzer. Rough forgings began to be turned out in heavy quantities by the Mesta Machine Co. in the spring of 1918, while the Watertown Arsenal, the other contractor, reached quantity production in rough forgings in September, 1918. At their special recuperator plant at Detroit the Dodge Bros. turned out the first finished 155-millimeter howitzer recuperator in July, 1918, and went into quantity production with them in September, producing 495 in the month of November alone, and turning out up to the end of April, 1919, the great number of 1,601 of them. Next in order of time to be conquered as a factory problem was the 155-millimeter gun recuperator. The rough forgings at the Carnegie Steel Co., the sole contractor, were in quantity production in the spring of 1918. The first of these recuperators finished came from the Dodge plant in October, 1918; and although 30 issued from the plant and were accepted before the end of the year, quantity production may be said to have started on January 1, 1919, when the factory began producing them at the rate of more than four a day. In March the high mark of 361 recuperators was reached, and the total production up to the end of April was 880. The heavy 240-millimeter howitzer recuperator was third to come into quantity production. The rough forgings were being turned out in quantity in the spring of 1918 by the Carnegie Steel Co., while the Watertown Arsenal, the other contractor, produced a number of these rough forgings in August, 1918. The two contractors for finishing and turning out the complete recuperators were the Otis Elevator Co., at its Chicago plant, and the Watertown Arsenal. The arsenal produced the pilot recuperator in October, 1918. In January the Otis Elevator Co. produced its first four, while quantity production began in February, 1919, both contractors that month sending out 19 recuperators, a number which may be regarded as good quantity when the size of this mechanism is taken into consideration. Both plants together in April turned out the large number of 89 recuperators for the 240. Last to come through to quantity production was the hardest of the four to build, the one that promised to defy American industry to build it at all--the 75-millimeter gun recuperator. The two contractors for the rough forgings for this recuperator were the Carbon Steel Co. and the Bucyrus Co. The Carbon Steel Co. was in large series production of them in the spring of 1918, and the Bucyrus Co. reached the quantity basis of manufacture in October, 1918. In that month alone both contractors together turned out 1,305 sets of forgings.