In 1939, Britain and France fought without American participation, while Britain's war effort depended heavily on imperial resources and maritime connections. If the conflict became another World War I-style trench war, trained troops and reserves from across the empire could be essential. Those formations mattered only if shipping could carry them to the theaters where they were needed. The same sea lanes kept supplies and currency moving through Britain's economy, so even a temporary interruption imposed costs.
Chapter · 2:53-4:10
Imperial shipping sustained Britain's war effort
British sea lanes carried troops, supplies, and economic resources from across the empire, making their protection central to the war in 1939.