Abstract: An arm and safety switch for ammunition rounds, such as a 120 mm multipurpose tank round, senses launch detonation pressure. The switch will not arm the projectile if the pressure detected is less than or equal to a first predetermined pressure characteristic of a misfire, and will arm if the detected pressure is greater than or equal to a second predetermined pressure characteristic of a successful launch. An efficient, reliable method and mechanism operate to discriminate between successful and unsuccessful projectile launch and use that information to arm or not arm the projectile.