It got a lot to do with the way the para's are dropped, if the C-47 passes over the field @ 1000ft and drops them in a straight line they are easy meat for a fighter and most of the time you can kill them all in 1 or 2 passes before they hit the ground. A much safer way (maybe less historic) is to come in low with a bit of speed and head for the tower (or is it the map room ?), when you are almost on top of it zoom climb and get the para's out as fast as you can on the way up, Before you stall all the troops are out and you can rudder over and head back down. By now the first para is landing next to the tower with the rest will land in about the same spot one after the other, they dont have far to go and are much harder to kill than a nice long line of chutes.