Father's letter to newly enlisted son in RAF

My Grandad, Maurice Lee, wrote this letter to his son, Geoff, my Dad, when he enlisted in the RAF. Nora is Geoff's younger sister [by 13 years] referred to in the letter as "Dickie". Dad then went on to Cairo, where he was stationed during the war in the RAF. He was not a pilot, as his eyesight was not good enough, but he served with honour behind the scenes.