The Disaster of Trying to Help Greece
One of the worst military disasters to befall the British Empire in World War Two was their brave yet completely disorganized and futile effort to assist Greece in beating back the German invasion of that country. While everyone knew a German attack was imminent, Greece continued to maintain their neutrality while inviting the British to send armed forces to their country. But their neutrality compelled them to continue diplomatic relations with Germany so as not to give the Germans any excuse for accusing them of hostile acts. (Such as expelling German diplomats.)
This allowed German military and naval attaches to stand in full view of the British ships debarking troops and equipment into Piraeus, the main port for Athens. And the Germans counted all these soldiers to the last private and all the equipment to the last tank and all the supplies to the last cartridge.