CIB, WDC 408 44 = Combat Infantryman Badge awarded per War Department Circular Number 408 of 1944.
MKM R = indicates he qualified as Marksman with the standard service rifle (probably the Springfield '03) in May 1942.
Under the Selective Service Act of 1940, certain qualified individuals were inducted to serve a one-year training period, after which they were released from active duty but subject to recall in the event of war.
Those serving on active duty on 7 December 1941 were extended "for the duration" while most of those who had been released from active duty prior to that date were recalled to duty (also "for the duration"). Langston was apparently among the former.