If we're talking from a tactical perspective, knowing is defintely half the battle. Only a fool would lead his troops in the enemy's direction without first knowing about them, their capabilities, combat deployement, etc.
I think the second thing is heart. Knowing is the knowledge of what you need to know to survive. But heart (and by heart I mean courage, bravery, a compassion for your fellow soldiers etc.) is the other half which is the physicality of the military operation itself.
You can't do much without tactics (knowledge) but can't do anything without heart.