Tuhia he tomokanga mo tenei pene - I whanau a O'Shannon i Marino, Dublin, Ireland, i te 23 o Akuhata 1928, te tama a Cathal O'Shannon (Sr.), he Socialist me Irish Republican. I whiwhi ia i tana maatauranga i te Kura o Colaiste Mhuire, i Parnell Square, Dublin. Ahakoa nga kaupapa tōrangapū a tona papa, i te 16 o ona tau o O'Shannon i tuku mo te ratonga pakanga me te Royal Air Force i Belfast i te 1945 i te Pakanga Tuarua o te Ao, ma te whakamahi i tetahi tiwhikete whanau tinihanga hei huna i te mea he iti ake te pakeke mo te whakauru ki nga Rererangi o Ingarangi. Whai muri i te whakangungu a te roopu rererangi i tukuna ia ki te Rawhiti ki te Rawhiti, hei kaipatu pupuhi i muri i te kaiwhakataunga rererangi Avro Lancaster ki te whai waahi ki te Whakatairanga o Burma, engari i mutu te pakanga me te hinganga o te Emepaea Hapanihi
i mua i te mea ka hiahiatia ia ki te rere i nga rerenga whawhai.