Regarding German defensive lines. In the campaign in NW Europe, the Germans were caught on the 'wrong side of the river', because they were not to retreat. A mile retreat behind a river barrier would have delayed the Allies. Retreat=Defetialism. Now that is a dangerous road to walk.

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'We march. The enemy is retreating in transport. We follow on foot.' Lt.Neil McCallum 5/7 Gordons 19th November 1942