the 315 prefix was Diehl, they later became part of Ryobi (1988), Sears kept the prefix the same, so 315 can also mean Ryobi...
The all aluminum case Sabre saws are from around the 1950's
There is very little info on stuff made by Diehl, I suspect they were only a Sears supplier for a short period of time for small power tools...