Procurement of the 4.2-Inch Mortar

C Facilities Inspec Br for Dir, Prod Div, ASF. 22 May 43, sub Fillers for M47, or M47A1, and M69 Incendiary Bombs. ASF 471.6 Grenade Bombs. 

Unless otherwise indicated, this section is based on the Histoiy of the Chicago CWPD, 1 July 1940 through 31 December 1944, pp. 59-62, 1 January 1945-15 August 1945, pp. 51-52, and interviews with M. A. Bell, manufacturer of the 4.2-inch mortar (4 April 1957) and with the following key officers who were intimately acquainted with the manufacture of the mortar Col Gilbert C. White (4 April 1957), Lt Col Walter E. Spicer, Jr., (28 April 1955), Lt Col J, S. Entriken (21 June 1956), and Lt Col Robert C. Hinckley (15 October 1956). 

ACofS G-3 for TAG, 5 Sep 41, sub Chemical Troops, G-3/46556. The 19 July 1938 directive, among others, is referred to in Memo, ACofS, G-4 for AC of SWPD, 28 Mar 40, sub Lack of Chemical Warfare Weapons and Supplies. G-4/29895-1. 

The Bell Machine Co., a manufacturer of custom-made woodworking machinery in peacetime, undoubtedly did not foresee the tough job it would encounter in rifling the barrel of the mortar. The 4.2-inch barrel was unique in U.S. Army munitions in that it employed ratchet type rifling rather than the simple spiral rifling employed in small arms and in most field pieces. This feature seriously complicated the broaching of the barrel, as the Bell Co. and the CWS inspectors from the Chicago district shortly came to learn. 

Early in 1942 a broaching machine arrived at Oshkosh from Edgewood. Some 56 barrels had been rifled on this machine when it was discovered that 4 inches of the rifling toward the muzzle were defective. Little progress could be made in manufacturing the barrel until a suitable broaching machine was obtained. To overcome the difficulty the OC CWS, awarded a contract to the American Broach Co., Ann Arbor, for the design of a new 35-ton hydraulic broach. This broach when put into operation was to prove very satisfactory, but it was not ready for installation at the Bell Machine Co. until June 1943. Meanwhile the manufacture of the barrels had been delayed for more than a year. Only 823 barrels were manufactured in 1942, compared to 2,002 in 1943 and 2,600 in 1944. By October 1944 the Bell plant had a capacity of 800 to 1,000 mortars a month, but the production schedule called for only 200.  

---