With regards to responding to ambush, there's one very clear and very hard and very fast rule of being ambushed - in the quickest possible fashion, orient every gun in your squad towards your attackers and have EVERYONE dump 20-30 rounds in that direction (yes, this will only work against players, but honestly, how often do we get ambushed by AI, this past Sunday's convoy non-withstanding?). It doesn't even really matter if any of those bullets hit - the sheer volume of fire achieves fire superiority, which can then be used by your fire team or squad leaders to direct the team to a new course of action, whether that be withdraw under smoke, form base of fire so other elements can flank, or straight up assault into the teeth of the ambush.
If you're John Q. Assistant Automatic Rifleman, and you see the enemy ambushers firing, and no one has called them out yet, get on squad comms and give a contact report. "Ambush! Front Right! By the two-story building!" gets everyone properly oriented and laying fire on the enemy.
That would be the bare-bones "response to ambush." If you think that sounds suspiciously like "Just kill the f***ers," then you'd very much be right! Specifying doctrinal responses (when to assault into its teeth, when to withdraw under smoke, when to form base of fire in the killzone) is more complicated than we really care to go. Basic fire superiority and letting the FTLs / SLs figure things out is good enough for FA!
~ Ferrard
P.S. If there is sufficient interest, then I could be convinced to actually go forward with training for the doctrinal responses... but it will take chocolate. Or strawberries. Or a mix thereof. Be creative.
