Combat rounds are 12 seconds long. The initiative is simple, but the wound system is harsh. There are no "hit locations" in the base rules (introduced later), but there is a "Major Wound" rule: If you lose half your HP in one blow, you are knocked unconscious and will bleed out in 3 rounds. The PDF explicitly tells Keepers: "Let the dice fall where they may."
There is a lean, mean purity to the 1st edition. Modern CoC gives you push rules, luck spends, and optional pulp modes. 1st edition gives you a d100, a bad feeling about that attic, and a character sheet with a "Cthulhu Mythos" stat that actively hurts you . call of cthulhu rpg 1st edition pdf
But if you bring it to a table of horror fans ? It’s perfect. Combat rounds are 12 seconds long