By the time they are aware that an attack is underway all they will accomplish by lowering the gates/raising the drawbridge is trapping victims inside and rescue efforts outside.
I guess this means that there will be no more kamikazi plane attacks - ever! So glad to find out that DHS/.mil has figured that out.
L'Enfant had the plan for how to prevent the enemy/mob from getting to the gates. I just wonder if the .mil still carries grape and chain shot rounds any more.