Between May 1940 and the summer of 1941 the British people expected a German invasion that, had it succeeded, would have enslaved them into the Nazis' racist war. This period saw an unparalleled effort to prepare the defence of the UK against invasion. Scotland's nationally important heavy industries, vital Royal Navy bases, and one of the UK's key ports, were very vulnerable to the sort of airborne attack that had devastated the defences of Belgium. Everyone was certain that a Fifth Column of Nazi sympathisers and agents was working actively to spread rumours and despair, and to aid the invasion forces, and in reality the country was far from united.