Gatacre married Winifred May Palmer at the Presbyterian Church in Mosman in January 1933. Soon after, the couple left for Britain, where Gatacre was to undertake specialist navigational training with the Royal Navy. He completed his advanced navigational course in 1937, having undertaken his training aboard and , including navigational training off the Spanish coast during the Spanish Civil War. He joined the crew of in later 1937, and was promoted to the rank of lieutenant commander in January 1938. He was serving aboard at the start of the Second World War, and later served aboard , and . He was the navigator aboard HMS "Rodney" and was involved in the hunt for and sinking of the German battleship "Bismarck". For his "accurate navigation and judicious selection of courses" during the hunt, he was awarded the Distinguished Service Cross in the 1941 Birthday Honours.