I know that there are 4 branches of land doctrine - the top left 1 and right 2, and the bottom left 3 and right 4 (names I can't remember), once you follow through one the rest are out-of-question and the only thing you can do to boost you troops performance is try rushing research of that branch (no more get-all-doctrines research as in HOI1). If I recall correctly, the German has the bottom left one 3. What advantage does it give? Anything not good about it? If I'm using huge manpower country like SU and China, which one is the best? What about France and England?