Defense in depth was actually invented by the Germans in World War One:<p><a href="http://en.wikipedia.org/wiki/Trench_warfare#World_War_I:_trench_defensive_systems" rel="nofollow">http://en.wikipedia.org/wiki/Trench_warfare#World_War_I:_tre...</a><p>As were the concepts of Schwerpunkt and penetration. These are clearly described in, e.g., Rommel's book about his WW1 infantry operations (<a href="http://en.wikipedia.org/wiki/Infantry_Attacks" rel="nofollow">http://en.wikipedia.org/wiki/Infantry_Attacks</a>).
Fortunately, that defense was never required - 70 years to the day since the famous speech:<p>"Never in the field of human conflict was so much owed by so many to so few."<p><a href="http://en.wikipedia.org/wiki/Never_was_so_much_owed_by_so_many_to_so_few" rel="nofollow">http://en.wikipedia.org/wiki/Never_was_so_much_owed_by_so_ma...</a>