After attending the coronation Fleet Review for George VI at Spithead in 1937, Medway Queen was converted to oil-fired steaming by Wallsend Slipway & Engineering Company in 1938.
Requisitioned by the Royal Navy as a minesweeper, she was renumbered No J 48 (N 48), serving for the duration of World War II in the 10th minesweeping flotilla, protecting the English Channel.