mckellar grew up and joined the family business in his native scotland, but in 1936, aged 24, he joined the raf and began pilot training. he completed his training in 1938 and was assigned to no. 602 (city of glasgow) squadron raf, an auxiliary unit. in 1939 he converted to the supermarine spitfire fighter. he experienced his first combat with no. 602 squadron, credited with two victories soon after the outbreak of war in 1939 against german bombers attacking royal navy ships and installations over northern britain during the "phoney war" period. mckellar's first victory earned him the distinction of being the first pilot to shoot down a german aircraft over the british isles during the war.