Initially Unwin served aboard HMS Iron Duke on the staff of Admiral John Jellicoe but in February 1915 he took command of the torpedo gunboat HMS Hussar which had operated as a despatch vessel for the Commander in Chief, Mediterranean and was now a minesweeper.
In 1915, when planning began for the amphibious landing on the Gallipoli peninsula, Unwin proposed beaching the 4,000 ton collier SS River Clyde on the narrow beach beneath Sedd el Bahr at Cape Helles, known as V Beach, thereby allowing 2,000 troops to be landed together.