Sorry guys, it seems to be a little different:
Not based on experience, simply by reading the wiki, it would appear that it does not:
"Terrain Penalty Reduction:
+30.00%
(Applied after summing all other terrain modifiers, not applied to
terrain features)
Link to relevant part of wiki:
Commander Assignable Traits"
As stated correctly, the trait is NOT applied to terrain features.
But you find that the 15% penalty of forts is listed as a terrain feature!
But we have to take into account: the wiki refers to versions 1.5 / 1.8.
I looked into the game-files and found " forts" only as building ( called "bunker" without any "modifiers" which provide penalties or buffs ); forts were not listed as "terrain" or terrain-modifiers.
So I let my computer searches the whole HOI4 datas for "fort" and "bunker".
Result: the word fort ( or forts, fortress etc ) appears in many files, most wiki-html, foci, ideas, events etc. Some units like engineer and AT-units ( like TD ) get boni for attack/defense, some traits like fortress-buster too.
Similar was the search for bunker.
We all know that forts give defense-boni, but I couldn't find a file to verify.
Confusing....
