I know this is a Light Blue forum and I'm about to ask an army type qustion, so excuse me while I put my body armour on
! This is, however, a serious question (research for an OU essay) and I'm sure some knowledgeable chap here will have the answer. I seem to remember from somewhere that, to be successful, an attacking force should outnumber the defending force 3:1 - anyone got any reference for that? Here's hoping.
CB