A P.38 hard shell holster that has a RB Number to identify the maker rather than a maker code.  Not much is known about the RB numbers.  It was a late war change but the military code seems to have been used right up to the end on a lot of items so it's possible the directive went out to change to the RB Numbering system but a lot of makers just didn't get the change made before the war ended.   Since this is a hard shell and with the RB Number I feel this holster was made in the latter part of 1944.  Using the RB Number alone as a clue, it could have been made in 1945 but I know of no hard shells that can be documented to have been made in 1945. RB Numbering also shows up on soft shell holsters.