Sir William Congreve, political propagandist, lawyer, inventor, and Chief Equerry to King George IV, was one of the foremost military salesmen of the early nineteenth century.

When England faced the overwhelming might of Napoleonic France, Sir William championed the potential of secret weapons, notably gunpowder rockets, mass-produced by the latest advances in manufacturing science. His was a world of fireships, bomb brigs, invasion fleets, experimental warfare, espionage, and the intense hostility of rival “projectors”.

By turns acclaimed, derided, libelled and sued, Congreve...