Pretty sure the idea is that most of the General's skills represent tactics (better operations in the desert, etc.), whereas the Field Marshall represents strategy, operating from a staff headquarters further in the rear (or even in Washington/London); at that level any particular familiarity with whatever particular terrain or what not has to be filtered through so many layers of intermediate officers and bureaucracy (with the resultant delays in orders, and difficulties of overseeing as many details) that it is effectively meaningless. On the other hand, that level of scale allows for things like rationalization of supply chains and the like, which is where the Field Marshall shines).While this may be true in certain cases, I just don't understand why they should all immediately forget the skills that got them the promotion in the first place...
Perhaps instead of removing the old skills, being promoted should open up 3 new slots for the field Marshall traits as well? This will simulate learning new tactics on a grand strategy scale, not just small scale battle strategy.
It's not like Eisenhower could realistically call up and say "that battery would have better cover if it were 5 meters to the left; make it so."
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