Rubuta ci gaba don wannan sakin layi - Cassels ya yi aiki a yakin duniya na biyu, inda yake aiki a Ingila, kuma ya halarci wani ɗan gajeren lokaci a Kwalejin Staff, Camberley. A watan Mayu 1940 sai ya zama babban brigade tare da rundunar Sojojin Yankin (TA), Brigade na 157 na Sojoji, wanda Brigadier Sir John Laurie ya ba da umarni, tsohon Kwamandan Kwamandan Cassels (CO) a cikin 2nd Seaforths, wani ɓangare na Manjo Janar James Drew na 52 (Lowland) Infantry Division, wanda aka aika zuwa Faransa a watan Yunin 1940 don ƙarfafa sojojin Faransa a bayan da aka kwashe sojojin Birtaniya (BEF) daga Dunkirk. Rundunar Cassel, ta farko daga cikin brigades na 52 na Division da suka isa Faransa, ba da daɗewa ba bayan isowarsu, an umurce su da su kafa dama na rundunar sojojin Faransa ta goma a Conches, Normandy. Duk da haka, an yi la'akari da halin da ake ciki ba shi da bege kuma an janye brigade na Cassel daga baya ta hanyar Cherbourg a ranar 18 ga Yuni. Faransawa sun sanya hannu kan yarjejeniyar tsagaita wuta ta biyu ta Compiègne
bayan 'yan kwanaki.