In the story, the Sutherland rescues naked and emaciated Frenchmen from a makeshift raft.
The men had been prisoners of war who had been confined to the deserted island of Cabrera.
With no ports, the Spanish authorities had left the prisoners unguarded, and the only care they provided were food shipments.
Through his superior seamanship, Hornblower is able to shoot a line to the prisoners and use it to let them tow to shore a casks of food from his own ship's stores.
Cabrera is a real island and Spanish authorities did confine French prisoners there.