JW 51B comprised fifteen British, American, and Panamanian merchant ships, most around 6,000 gross registered tons. An empty convoy was returning at the same time because ships had to reach loading ports before they could carry more supplies. Empty merchant ships still made valuable targets: sinking them disrupted later sailings even when no cargo was lost. Rapid Liberty ship production made an empty hull easier for the Allies to replace than the combined loss of ship and cargo. Destroying either convoy would still disrupt operations and produce headlines about another convoy disaster.
Notable Point · 45:47-48:58
Why empty return convoys still mattered
Loaded outward convoys carried both ships and cargo at risk, while empty return convoys kept merchant hulls available for future sailings.