Libyan campaign

During Operation Compass, the British offensive against Italian forces in Egypt and Libya, No. 274 Squadron was regularly in action, carrying out patrols over and in front of the advancing troops.^[7] On 9 December 1940, the opening day of the offensive, Mason achieved his first aerial victories, one of five pilots sharing in the destruction of two Savoia-Marchetti SM.79 medium bombers and damaging of three others in the Sidi Barrani area. Later in the day he flew another sortie, engaging and damaging a Fiat CR.42 fighter. Two day later he destroyed a CR.42 over Sidi Barrani and then on 15 December, shot down a SM.79 in around the Bardia-Sollum area. He destroyed another CR.42 on 16 December over Bardia although military aviation historians Christopher Shores and Clive Williams suggest that this may have been officially recorded as being a probable.^[2]

On 22 December, Mason shot down a SM.79 to the west of Fort Capuzzo and also damaged another of the same type. The next day he destroyed a Caproni Ca.310, a twin-engined reconnaissance aircraft over El Gubbi.^[2] By this stage of the campaign, the squadron was also involved in making ground attacks on Italian troops and carrying bomber escort missions.^[7]

During January 1941, Mason regularly carried out intruder sorties into Italian-held territory in Libya, targeting airfields of the Regia Aeronautica (Royal Italian Air Force). On these often successful sorties, he was typically only accompanied by one pilot. He destroyed a pair of CR.42s over Gambut on 3 January. He and his fellow pilot strafed an airfield at Gazala on 8 January, and between the two of them shared in destroying thirteen SM.79s. The following day, on a sortie to Martuba, he shot down a CR.42. He also caught and destroyed a Fiat CR.32 fighter on the ground. On 10 January he destroyed a SM.79 over Derna and damaged a Fiat G.50 fighter.^[2]

On 26 January Mason shot down three CR.42s to the west of Martuba. These successes were followed four days later with another CR.42 destroyed, this time over Benina Airfield.^[2] The following month the squadron returned to Egypt for a period of rest.^[7] Mason was noted for his eccentricities; he had grown a dense beard and acquired the nickname 'Imshi', this being an Arabic colloquialism for scram, which Mason supposedly used to deter peddlers. He was by this time also the leading Allied ace of the Libyan campaign.^[2] Officially credited with thirteen aerial victories, he was subsequently awarded the Distinguished Flying Cross. The citation, published in The London Gazette on 11 February 1941, read:

In January, 1941, this officer destroyed three of a formation of nine enemy aircraft. He has continually shown a fine fighting spirit and has contributed materially to the heavy losses caused to enemy aircraft. He has shown outstanding courage and initiative and has destroyed at least thirteen hostile aircraft".

— London Gazette, No. 35073, 11 February 1941^[8]

Malta

In March, Mason led a flight of Hurricanes to the Mediterranean island of Malta to supplement the defensive fighter force stationed there. Flying with No. 261 Squadron on 13 April, Mason engaged and destroyed a Messerschmitt Bf 109 fighter of the Luftwaffe. However he was attacked in turn by a Bf 109 of Jagdgeschwader 26 (Fighter Wing 26) and had to ditch his aircraft in the sea, breaking his nose in the process. Rescued, he was repatriated to Egypt for medical treatment.^[2]

Later war service

In July, following his recovery, Mason was promoted to squadron leader and assumed command of No. 261 Squadron which, having been briefly disbanded, was reforming with Hurricanes in Habbiyana in Iraq at the time. In August he led the unit in the Allied occupation of Iran. Its primary duty was patrolling over the ports at Abadan and Khorramshahr but it also intercepted aircraft of the Imperial Iranian Air Force. On 26 August Mason shot down a Hawker Nisr light bomber. Later in the year the squadron operated in Palestine.^[2][9]

At the start of 1942, Mason was posted back to Egypt to command No. 94 Squadron.^[2] His new unit was non-operational at the time, due to being in the process of reequipping with P-40 Kittyhawk fighters.^[10] Its first operational sortie with the Kittyhawks was on 15 February, when Mason led a ground attack mission against a Luftwaffe base at Martuba. His aircraft was shot down by Otto Schulz from Jagdgeschwader 27 (Fighter Wing 27) and he was killed.^[2][11] He is commemorated on the Alamein Memorial in Egypt.^[1]

Shores and Williams credit Mason with the sole destruction of fifteen Italian and German aircraft, with another two shared with other pilots. He also damaged six aircraft, three of which were shared with others. Fourteen more aircraft, all Italian, were destroyed on the ground although only one was solely credited to Mason; the others were shared.^[2]