On Spitfires

Scotland was in range of Nazi Germany's long-range bombers and reconnaissance aircraft. The Luftwaffe's main operations being mainly against the Royal Naval Home Fleet anchored in Scapa Flow. The squadron was operational with Spitfires in time to intercept the first German air raid on the British Isles on 16 October, when it shot down a Junkers Ju 88 bomber into the Firth of Forth north of Port Seton – the first enemy aircraft to be shot down over Great Britain since 1918, and the first RAF victory in the Second World War. It remained on defensive duties in Scotland until 27 August 1940, when it moved on rotation to Southern England, based with No 11 Group at RAF Hornchurch, where it was operational from 27 August 1940 for the remaining months of the Battle of Britain.

Two days after the squadron became operational in southern England, Carbury claimed the first of his 15½ victories, becoming the fifth highest scoring fighter ace of the battle. He was awarded the Distinguished Flying Cross and Bar with 603 Squadron during the battle. P/O R. 'Ras' Berry claimed some 9 (of an eventual total of 14) victories during this time, while P/O 'Sheep' Gilroy claimed over 6 victories. Plt Off Richard Hillary (5 victories) was shot down on 3 September in combat with Bf 109s of Jagdgeschwader 26 off Margate at 10:04hrs – rescued by the Margate lifeboat, he was severely burned and spent the next three years in hospital, during which time he wrote a book, The Last Enemy.^[8] By the end of the Battle of Britain, according to more recent academic research including the scrutiny of German records, 603 Squadron were identified as the highest-scoring Battle of Britain fighter squadron.

Returning to Scotland at the end of December, Carbury damaged a Ju 88 on Christmas Day over St Abb's Head, before leaving squadron in January 1941 as an instructor at the Central Flying School. In May 1941, the squadron moved south again to take part in sweeps over France (termed "rhubarbs"), until the end of the year.

After a further spell in Scotland, No. 603 left in April 1942 for the Middle East where its ground echelon arrived early in June. Concurrently, Flt Sgt Joe Dalley moved from the squadron to PRU duties and flew a Spitfire PR direct from RAF Benson to Malta, joining No. 69 Squadron RAF to become one of four pilots known as the "Eyes and Ears" on the Island. The squadron's aircraft were embarked on the U.S. aircraft carrier Wasp and flown off to Malta on 20 April to reinforce the island's beleaguered fighters. After nearly four months defending Malta, the remaining pilots and aircraft were absorbed by 229 Squadron on 3 August 1942.

On Beaufighters

At the end of June 1942, No. 603's ground echelon had moved to Cyprus, where it spent six months as a servicing unit before returning to Egypt. In February 1943, Bristol Beaufighters and crews arrived to begin convoy patrols and escort missions along the North African coast and in August sweeps over German held islands in the Aegean and off Greece began. Attacks on enemy shipping continued until the lack of targets enabled the squadron to be returned to the UK in December 1944.

Spitfires again

On 10 January 1945, No. 603 reassembled at RAF Coltishall and by curious coincidence, took over the Spitfires of No. 229 Squadron RAF and some of its personnel, the same squadron which had absorbed No. 603 at Ta' Qali in 1942. Fighter-bomber sweeps began in February over the Netherlands and continued until April, when the squadron returned to its home base at Turnhouse for the last days of the war. On 15 August 1945, the squadron was disbanded.