Whakaotihia te rerenga e whai ake nei: I mahi a Cassels i te Pakanga Tuarua o te Ao, i te wa e mahi ana ia i Ingarangi, ana i uru ia ki tetahi akoranga poto i te Whare Wananga o Staff, Camberley. I te marama o Mei 1940 ka riro ia hei rangatira pirihimana me tetahi waahanga o te Army Army (TA), te 157th Infantry Brigade, i whakahaua e Brigadier Sir John Laurie, i mua ko Cassels's Commanding Officer (CO) i te 2nd Seaforths, he waahanga o te 52nd (Lowland) Infantry Division a Major General James Drew, i tukuna ki Parani i te Pipiri 1940 ki te whakakaha i te ope French i muri i te wehenga o te British Expeditionary Force (BEF) mai i Dunkirk. Ko te parirau a Cassel, te tuatahi o nga parirau o te 52 o nga wehenga i tae ki Parani, i muri tata mai i tana taenga mai, i whakahaua kia hanga i te tika o te French Tenth Army i Conches, Normandy. Heoi, i whakaarohia te ahuatanga kaore he tumanakohanga ana ka mutu te brigade a Cassel i te 18 o Pipiri i roto i Cherbourg. I hainatia e te Wīwī te
Ko te wehenga tuarua o Compiègne i nga ra i muri mai.