Airborne operations have often been called a vertical envelopment, and therein lies one of the best descriptions of their value. The essence of an envelopment is to pin the enemy in place so that it can be destroyed. A strong enemy force to one's rear disrupts supplies and communications and makes one more vulnerable to an attack from the front. It also has a major psychological impact. One of the certainties upon which soldiers rely is that everything to their front is the enemy and everything to their rear is friendly. It helps distinguish who to fire on and who to assume are reinforcements. To an aggressor the value of airborne troops, used properly, far outweighs their numerical strength. It would almost certainly be false to say that the German invasion of France and the Low Countries in 1940 could not have succeeded without the paratroops and their glider-borne comrades; but it would certainly have been made more difficult. Bruce Quarrie tells the story of the German airborne troops of the Second World War backed by numerous contemporary photographs and eight full page colour plates by Mike Chappell.