"and a pox on those that let only 3 of our troops man a checkpoint in that hellhole"
True. There is a concept out there called "guardian angel" and it is SOP for the Marine Corps and this is why.
There were more than three. The rest of them took off after the original hit and run raiders, leaving the three at the checkpoint. Whereupon the second wave hit. It's called a feigned withdrawal, and it's literally one of the oldest tricks in the book--it was ancient when the Romans used it. And it still works, unless your troops have iron discipline.