Why convoys disrupt just-in-time shipping

A merchant ship must wait for its convoy's departure and sail at the formation's set speed, undermining business models built on maximum utilization and minimal stocks. Shipping companies therefore resisted convoy systems and even the naval procurement needed to protect them during both world wars. Large groups then reach port together, producing a surge of cargo followed by a decline until the next arrival. Ports designed for continuous turnover can be overwhelmed when scores of ships seek berths at once. British preparations before the Second World War included warehouses and storage intended to absorb this feast-and-famine pattern.