I te tau 1941 ka uru ia ki te Royal Air Force, a, i te hotoke ka rere whawhai ia ki te No. 121 (Eagle) Squadron, i hangaia e nga kaihauturu Amerika. Pilot Officer Mahon kino toru toa Tiamana me e rua Focke-Wulf Fw 190s i April me te Messerschmitt Bf 109 i Mei, i mua i te kaute i tona wikitoria tuatahi whakapumautia o te rua Fw 190s, i hinga i roto i te Saint-Omer rohe, i runga i Pipiri 8, 1942. I te 31 o Hōngongoi i whakangaromia e ia ētahi atu Fw 190 e rua i runga i te rohe o Berck-Sur-Mer, ā, ka noho hei rangatira i a ia e hipoki ana i te whakaekenga o te commando ki Dieppe
I te 19 o Akuhata 1942, ko tana 98 o nga rererangi rererangi rererangi. I te 08:30, i te rere i tana Spitfire Vb, i tapaina ko "Barry", i koperea e Mahon tetahi Fw 190 me tetahi atu Fw 190 i mua i te pa mai o tana rererangi ka akiaki ia ki te whakaora i te waka rererangi e tahuna ana. I te taenga atu ki te moana, ka mauheretia ia. Ahakoa i tukuna e Mahon he kereme mo te patu i nga Tiamana e rua i taua ra, kotahi anake te nama i whakawhiwhia ki a ia i muri o te pakanga. No reira, mo te rekoata o te rima kua whakapumautia, e rua pea me te toru kua pakaru i Mahon i whakawhiwhia ki te British Distinguished Flying Cross i te tau 1985.