Washington's Dirigible (Timeline Wars/John Barnes, No 2)
The almost-human Closers are waging a war of annihilation across a million alternate timelines. Crux Op agent Mark Strang is on special assignment to colonial America to track down a missing time agent. But in this version of reality, George Washington is Duke of Kentucky, and Britain's King George III has been replaced by a ruthless impostor. Strang's scheme to rescue the real king leads him into battle in the skies on both sides of the Atlantic.