This is book 5 of the "Richard Delancey" series.

This note contains spoilers for the book.

Steam ships; perhaps useful as tugs. An underwater vessel, named the Nautilus (66 years before Verne wrote his version).

And the Army of England, Napolean's invasion army, and its fleet. Operations around the Channel, including working with the spymaster for the area. Also continuing good relations with the smugglers.

An Admiral who is a bit uncertain, and actually listens to Delancey, and even gives him the credit for what he accomplishes.

And a wife who plays the role of a Captain's wife perfectly. That's because she came off the stage, an extremely unrespectable occupation for a woman (they're considered one step from whores; and in fact this one tells Delancey she's slept with seven men before him, which by period standards is quite high).