Rubuta ci gaba ga wannan sakin layi - Ya koma aikin soja kafin yakin duniya na biyu, an ba shi izini a matsayin jami'in matukin jirgi a cikin Royal Air Force Volunteer Reserve a ranar 25 ga Afrilu 1939. A ranar 17 ga Yuni, 1940, bayan da Marshal Philippe Pétain ya bayyana aniyarsa na neman yarjejeniyar armistice
, Air-Vice Marshal Arthur Barratt, Babban Jami'in Jirgin Sama na Sojojin Sama na Burtaniya a Faransa, ya aika da Grinnell-Milne a kan manufa don isar da wasiƙu ga shugabannin Sojojin Sama na Faransa, yana mai bayyana ƙudurin Burtaniya na ci gaba da yaƙi, da ƙarfafa su su yi haka a Arewacin Afirka. An kuma nada Grinnell-Milne a matsayin jami'in haɗin gwiwar Burtaniya ga Babban Kwamandan Sojojin Sama na Faransa Joseph Vuillemin, kuma an sanye shi da na'urar watsa rediyo ta hannu, alamun kira da lambobin. Grinnell-Milne ya tafi Bordeaux, sa'an nan kuma zuwa GHQ Faransa Air Forces a Agen. A can Vuillemin ya sanar da shi cewa ya fara aiwatar da canja wurin maza da jiragen sama zuwa Arewacin Afirka, amma yanzu ya karbi umarni don dakatar da duk wani motsi. Grinnell-Milne ya gano cewa yawancin manyan jami'an ma'aikatan sun yi murabus ga makomarsu, masu hanawa, ko kuma masu adawa da juna, kodayake ya lura cewa yawancin matasa da maza suna ɗokin barin Ingila. Ya bar Faransa a ranar 18 ga watan Yuni a cikin jirgin. Da zarar ya dawo London an nada shi jami'in sadarwa ga Janar Charles de Gaulle na Faransa, ya kasance tare da shi har tsawon watanni huɗu masu zuwa, kuma ya shiga cikin yaƙe-yaƙe na Dakar da Gabon. An daukaka shi zuwa jami'in jirgin sama a ranar 3 ga Agusta 1941. An cire Grinnell-Milne daga RAF (a zahiri ya yi murabus daga mukaminsa), yana riƙe da matsayinsa na jami'in jirgin sama a ranar 20 ga Yuli 1944. Daga nan sai ya koma BBC, ya kasance a can har zuwa 1946.