I just crunched a few quick numbers out of my DMG. Assume if you will a fairly standard level 6 AD&D fighter. He is in Plate +1 (AC 2), wielding a shield +1 (down to AC 0), and somehow gets another two steps of AC (Pro Evil spell, rings of protection, more potent enchantments on armor/shield, high dex, etc) for a final AC of -2. He has about 45 HP -- strictly average for a 16 CON fighter.
A 1 HD critter doing 1d6 damage will basically never kill him. It will take over 200 attacks to off our fighter. A 2 HD critter doing 1d6 damage does better, requiring about 80 attacks. A 4 HD critter doing 1d10 damage (like an ogre) needs about half that many.
Those monsters are basically only a threat to magic-users, thieves, and offensively focused fighters (no shield, for example). Even in large numbers they won't be able to seriously threaten our fighter.
OD&D Experience Levels
7 hours ago