Army Pamphlets from early 50's

I recently bought 4 Dept. of the Army Pamphlets printed between July of 1951 - Jan. '52. These appear to be from a series entitled "Historical Study". All relate to the Eastern Front, with such titles as "German Defense Tactics Against Russian Break-Throughs", "Rear Area Security in Russia" and "Operations of Encircled Forces". They have little to no wear on them (one is missing a binding).

Does anyone have any info on this series? Also, how much would these be valued at (if you can price this sort of thing)?