Other mistake: In the opening credits, Lewis Carroll is spelled incorrectly, as 'Carrol'. (00:00:30)
Other mistake: The day after informing Lady Barbara that he was married, Hornblower, in a rush to get home, orders the t'gallants set. But the ship, as shown in the prior scene, already has them set.
Other mistake: In all of its appearances, the British flag (also known as the Union Flag and the flag of the United Kingdom) is wrong. The flag's X-shaped red Cross of Saint Patrick is shown as (a) wide, and (b) centered on its white background, whereas on the actual flag, it is (a) thin, and (b) not centered on its white background, but rather off-center in a counter-clockwise direction.