Fine day. Cleaned ship in forenoon. Night defence sounded off about 11.45. Submarine reported in harbour. Great excitement. Sighted periscope about 12.20 going about 12 knots. “Queen Mary” opened fire with Maxim. We opened fire with 4″ lydite and common. Sunk her after a little while. Some of our shot richoceted (sic) on shore & did slight damage. Small kid hurt. (This was reported not to be a submarine, but no explanation was given as to what it was).