On the outbreak of the Second World War Blanch enlisted in the Royal Air Force. He was on guard duty at Christmas at the RAF depot in Heaton Park (not, he later said, "a prospect to quicken the pulse or engender much seasonal cheer"), and for lack of anything else to read he read the New Testament thoroughly for the first time in his life, and his hitherto mild adherence to Christianity was turned into firm evangelical faith. "This strange book spoke, its words glowed on the page, and I knew that from that moment my life was bound up for better or worse with the Man who is described there."