Why the Gironde was both vital and dangerous

The Gironde was roughly forty-seven miles long and between two and seven miles wide, with severe tidal currents that made a canoe approach physically punishing. Bordeaux and nearby ports were worth the risk because their distance inland complicated air and naval attacks and raised the danger of civilian casualties. Blockade runners brought Germany critical supplies through these ports, even though their cargoes formed only a small share of total imports. An estimated thirty or more German vessels, together with searchlights and shore defences, protected the approach. Canoe crews had to stop paddling to hide as patrols passed, adding delay to a journey already constrained by the tide.