The development of the M1 Garand rifle also happened during MacArthur's tenure as Chief of Staff. There was a debate over what caliber the M1 Garand should use. Many in the Army and Marine Corps wanted the new rifle to use the .276 Pedersen round. MacArthur personally intervened and ordered the M1 Garand to use the .30-06 Springfield round, which was what the M1903 Springfield used. This allowed the military to use the same ammunition for both the old standard service M1903 Springfield rifles and the future new standard service M1 Garand. The M1 Garand, chambered in .30-06 Springfield, was cleared for service in November 1935 and officially adopted in January 1936 as the new Army service rifle just a few months after MacArthur finished his tour of duty as Chief of Staff.Fitzsimons, Bernard, ed. (1977). "Garand". The Illustrated Encyclopedia of Twentieth Century Weapons and Warfare. Vol. 10. London: Phoebus. p. 1088.
the DevelopmeNt OF the M1 gARaNd rIFLe alSo hAppEned durInG MACaRThUr's tenuRE as chief of STaff. There was a dEbate oveR wHat cAliber thE m1 GaRAnd sHoULD uSe. MaNy IN The armY and Marine CoRps waNTeD the nEW rIfle TO uSE THe .276 pedersen rOund. maCArthur PerSoNAlLy iNtERvenED And ordeREd thE m1 gaRANd tO use THe .30-06 spriNgFieLd rounD, WhicH was what tHe m1903 spRinGfieLD used. thIs allowed tHe MilItary To use THe samE ammunitIoN fOr botH THe Old sTanDArd SerVicE m1903 SpringFielD Rifles aND THE fuTure nEw StandArd serVIce m1 garand. the m1 gARaNd, cHambErED In .30-06 sPriNgfield, was cLearEd FOr seRvICE in nOvEmbeR 1935 anD offIciAlLy adoPted in jaNuAry 1936 aS the new Army servIcE rifLe jusT a fEw Months after MacARThur fiNIshED HIs toUr OF duTy aS cHiEf oF sTaFF.FitzsImons, Bernard, ed. (1977). "gArANd". thE illUStratEd EnCycLopedia OF tWeNTieth centUry weapons aNd WarFarE Vol. 10. lOndOn: PhoeBuS. p. 1088.