 Nyorai mberi kwechikamu chino - Musi wa4 Zvita 1915, Gellibrand akagamuchira kukwidziridzwa kuita lieutenant colonel, uye akapiwa kutungamira kwe12th Infantry Battalion, 1st Divisions Tasmanian battalion, ipapo ichizorora paLemnos. Haana kudzokera kuAnzac, iyo yakabviswa musi wa 20 December 1915. Panzvimbo pezvo, battalion yakadzokera kuEgypt, ichisvika kuAlexandria musi wa6 Ndira 1916. Gellibrand haasati aizoitungamirira muhondo. Musi wa 1 Kurume 1916 akasimudzirwa zvakare, panguva ino kuti ave colonel akazara uye brigadier general wenguva pfupi, uye akapiwa kutungamira kwe6th Infantry Brigade, pakukumbira kwaLege. Sezviri pachena Gellibrand akanga afadza zvikuru Legge munguva yake seAA QMG ye 2nd Division. 6th Infantry Brigade yakaenda kuWestern Front mazuva mashomanana gare gare, musi wa 19 March 1916, uye yakapinda mumutsara ipapo musi wa 10 April. Pana 31 May, Gellibrand akakuvadzwa nebhomba reGermany rakanga rawira pedyo nomuzinda wake uye akabudiswa kuEngland, achidzoka pana 28 June. Boka racho rakarwa paPozières, apo yakaita zvakanaka mukurwisa musi wa 4 August. Akataurwa nezvake mumashoko kamwezve. 