 His brother George Losack preceded him into the Royal Navy and rose to the rank of admiral.As a lieutenant, Losack served on , the flagship of Admiral William Cornwallis, and participated in the enterprise to cut out "la Chevrette", a French corvette, of 20 nine-pounders and 350 men, from under the batteries in Camaret Bay, near Brest, on the night of 21 July 1801.Lieutenant Losack and Lieutenant Keith Maxwell were promoted to the rank of commander for their services in this enterprise.