The 15% guy is not a fleet commander, he is in the Military High Command. Also, as stated by LordofWar earlier if you are consistently fighting aircraft with your fleets it's possible that your admirals can gain the 'Fly Swatter' trait, which grants +10% Naval AA attack, in addition to their other traits.
Anyway. On to the good stuff:
Grand Battleplan Doctrine:
1. Grand Battle Plan: Max planning +30%
2. Trench Warfare: Max Entrenchment +10, Entrenchment speed +25%
3. Prepared Defense: Army: +10% Defense, +10 Organization
4. Grand Assault: Army: +10% Breakthrough, +5% Soft attack, Enables Well-planned attack
Assault (branch)
5. Mechanized Offensive: Motorized/Mechanized/Armor +15 Organization, Enables Blitz (This powerful doctrine is also the one shared with the Mobile Warfare (Mobile Infantry branch) and Superior Firepower Doctrines. As far as I understand with this teched you can switch over to those trees. Would like clarification from anyone in the know of if you just start advancing in the new tree from Mec. Off. onwards keeping your prior doctrines, or do you completely switch over to the new doctrine and pick new early doctrines.)
6. Assault Concentration: Max planning +20%, Enables Overwhelming Fire
7. Branch Inter-Operation: Army: +5 Organization
8. Assault Breakthrough: Breakthrough +10%, Enables Breakthrough
9. Central Planning: Max planning +10%, Planning speed +10%
10. C3I: Army: +5 Organization, Reinforce rate +40%
Infiltration (branch)
5: Infantry Offensive: Leg Infantry: ('foot' would've been a much better name) +10% Breakthrough, +5 Organization, Enables Infiltration Assault (Crossover to Mass Mobilization branch of Mass Assault Doctrine)
6. Armored Operations: Armor: Recovery Rate +10%, +10 Organization, Enables Blitz, Enables Elastic Defense
7. Infiltration Assault: Supply consumption -10%
8. Night Assault Tactics: Land night attack +25%
9. Attritional Containment: Army: +5 Organization
10. Infiltration in Depth: Recon: +1 Reconnaissance
Looks like an interesting doctrine. It aims to get the most out of your infantry, especially the Infiltration branch. The Assault branch will be the default route for many countries. Based on the methods of WW1 with new goodies like mobile infantry thrown in. Sits tight with its defensive bonuses, starts its long planning process while holding ground, unleashes an overwhelming assault with 160% planning bonus, profit. Originally thought I'd be on the first route out of this doctrine, but the idea of these unstoppable assaults where even the common infantry division is an engine of doom has me reconsidering my position. The Infiltration branch seems to be based on late WW1 German doctrine of penetrating deep with forward troops, not getting bogged down fighting enemy strongpoints, a bit like Deep Battle with an infantry focus. Infiltration looks like it will be the way to go for countries like Japan and Finland with their heavy focus on foot infantry. That +1 reconnaissance bonus assuming you keep up to tech as well, will give you a welcome advantage in picking counter tactics.
Will be back with lots more, just need to take a break from typing for now.