In 1939, an order for 24 Marcel Bloch MB.151 fighter aircraft was placed, but only 9 of the aircraft reached Greece, since the outbreak of World War II prevented the French from completing the order. The aircraft entered service in the 24th Pursuit Squadron (MD – Moira Dioxis) of the Air Force.
During the Italian invasion of Greece (1940) in the Second World War, although being severely outnumbered and counting only 79 aircraft against 380 fighters and bombers of the Italian Regia Aeronautica, RHAF managed to successfully resist the assault. On 2nd November 1940, a Breguet 19 intercepted the 3 Alpine Division Julia while it was penetrating the Pindos mountain range in an attempt to occupy Metsovo. On the same day, 2nd Lieutenant Marinos Mitralexis having run out of ammunition, aimed the nose of his PZL P.24 right into the tail of an enemy Cant Z1007bis bomber, smashing the rudder and sending the aircraft out of control.
However, after 65 days of war the RHAF had lost 31 officers, 7 wounded, plus 4 NCOs killed and 5 wounded. Meanwhile, the number of combat aircraft had dropped to 28 fighters and 7 battle worthy bombers. Still by March 1941, the Italian invasion had been successfully repelled, aided by the vital contribution of the RHAF to the Greek victory. During the Greco-Italian War the Hellenic Air Force shot down 64 enemy aircraft (confirmed) and claimed another 24. However according to other sources, the Italian Air Force lost 65 aircraft during the entire campaign against the Greeks and later the British, with 495 additional aircraft damaged.
In April 1941, the German Wehrmacht invaded Greece in order to assist the Italian assault. During this second wave of foreign invasion, the Luftwaffe eventually succeeded in destroying almost the entire Hellenic Air Force. However, some aircraft managed to escape to the Middle East, including 5 Avro Anson, 1 Dornier Do 22 and 3 Avro 626.
During the German occupation of Greece, the Air Force was rebuilt under the expatriated Greek Air Force Ministry based in Cairo. Three squadrons were built, operating under the command of the British RAF. These squadrons were the 13th Light Bombing Squadron flying Avro Ansons, Bristol Blenheims and Martin Baltimores and the 335 and 336 Fighting Squadrons flying Hawker Hurricane I and IIs and Spitfire V types. The RHAF squadrons in the Middle East flew a variety of missions, including convoy patrols, antisubmarine search, offensive patrols, reconnaissance, attack and interception of enemy aircraft. In Summer 1943, the Greek squadrons participated in the attack against the German Wehrmacht on the island of Crete and then from May to November 1944 in Italy. During those years, 70 Greek pilots were lost.
After Greece's liberation in 1944, RHAF returned to Greece and subsequently played a decisive role in the Greek Civil War, which lasted until 1950. By then, it was re-equipped with Supermarine Spitfire Mk IX, Spitfire Mk XVI fighters and Curtiss SB2C Helldiver bombers.