Maps of canals and anti-invasion defenses show how often the routes align. Canals offered continuous obstacles whose depth and crossing points defenders could survey in advance, making them natural positions for pillboxes and prepared resistance. Their military value came in addition to their transport role, although a canal line still depended on troops being mobilized and ready to hold it.
Chapter · 2:08:17-2:17:06
Canals as anti-invasion stop lines
British defense planners incorporated canals into layered stop lines because their known depth, banks, and crossings created predictable obstacles to an invader.