Jorn,

18 mines yes, but the number of torpedoes onboard can’t be more than six and it could be lower.

The base torpedo count for a UCII was four: a torpedo each in both the external bow tubes, and a torpedo in tube plus a reload for the stern tow. It could grow to be as high as seven by adding more reloads -- for the bow tubes, these would be lashed to the deck, and for the stern tube, internally, broken down into several pieces. It’s not a given though that UC 30 sailed with seven torpedoes though.

UC 30 is credited with torpedoing and sinking the British steam Hunstanton. It’s unknown whether she might have have fired and missed at additional ships.

Did they find reload torpedoes on deck?

Best wishes,
Michael