The Coastal class airship were created for underwater combat missions and were used by the Royal Naval Air Service (RNAS) during WWI. Its main task was the protection of maritime convoys from the German U-boats attacks and they were armed with 45kg or 50kg bombs or with 104kg depth charges. A variable number of 7.7mm machine guns were mounted for self-protection against enemy aircrafts. They did not have any mechanical means of underwater detection, so the surveillance was carried out by an observer who communicated the detections via radio. Six submarines were sunk by the Coastal class airships throughout the war, which may seem little, but their dissuasive mission was very successful, forcing to flee to any submarine with its mere presence in the area.
COASTAL class gallery and more info