WORK IN PROGRESS
When operating aircraft, managing speed is an important skill in using them effectively. In it's simplest form, squadron speed is managed with the W key (faster) and the S key (slower). Speed is also affected by commander skills, upgrades, etc.
There are two speed parameters to note: base or cruising speed, and maximum speed (as fast as you can go without NOS). Max speed is typically the base speed plus a fixed number (usually 35 or 40 kts, depending on the aircraft type).
There are three types of speed bonuses, those to base/cruising speed (e.g. "+N% to squadron cruising speed") and those to overall speed, both base and maximum (e.g. "+N% to squadron speed").
Base of all sqdns
"Squadron speed +2.5%"
Base of one type
"Bomber cruising speed +5%"
For instance, the BDT Destroyer bombers on Midway have an unmodified cruising speed of 131 kts, and thus a max speed of 166 kts (cruising +35). Mounting the unique Modified External Hardpoints upgrade (Bomber cruising speed +5%) gives 138 kts with a max of 173 kts (again, cruising +35).
Max of one type
"Maximum squadron speed +12.5%"
On Hakuryū, her J5N Tenrai bombers have an unmodified cruising speed of 152 kts, and thus a max speed of 192 kts (cruising +40). Mounting the unique Fuel Injection System upgrade (Maximum squadron speed +12.5%) gives the same cruising speed with a maximum of 216 kts! Training her commander in Bomber Flight Control (cruising speed +5%) increases cruising speed to 160 kts and maximum to 227 (base of 160 +12.5%).
Fighter / Interceptor Response
While not a speed boost per se, the Enhanced Reactions skill produces Fighters that are much more responsive to intruding enemies, giving them the effect of closing faster to air battle.
Back to the Barn!
In a similar fashion, the Hidden Menace skill has a similar indirect effect on speed.