Summary: Dramatised Navy Instructional film set onboard an unidentified nuclear submarine. The film lists the duties of Officer of the Day (OOD: the officer responsible for the safety of the ship and ship's company for a given day while in port) through the experiences of a sub-lieutenant taking his first duty. The items he is required to check as part of his duty and an exercise bomb threat are shown in particular detail. The type 22 frigate HMS Brilliant (F.90) also appears briefly.