"Captain Frederick Wentworth ... being made commander in consequence of the action off St. Domingo..." (ch 4)

What is this mysterious "action off St. Domingo?" The short version is that after Trafalgar, a French squadron was pursued to the Carribean, specifically offshore of St. Kitts in San Domingo. There it was defeated by the British forces on February 6, 1806.

The above painting of the battle hangs in the Maritime Art Museum at Greenwich. More information about the battle and the artist can be found at the link below.