Why wartime convoys assembled at Sierra Leone

What was transported from Sierra Leone to Britain during the convoy war?

Ships carried large quantities of raw materials and personnel, often after assembling at Sierra Leone from routes around the Cape and across the Indian Ocean.

Sierra Leone was one of several global gathering points in the British convoy system. Ships arrived from the Indian Ocean and around the Cape, assembled there, and then sailed north in escorted groups. Other convoys connected the Cape with Sierra Leone, allowing escorts and shipping to be staged and handed over. The port mattered as an organizing node as well as a source of personnel and raw materials.