There had been novels in England foreseeing enemy invasion as far back as The Battle of Dorking, serialized in Blackwood's Magazine in 1870. From 1902, when Germany had decided to build a battle-fleet to equal England's, the idea of a blitz invasion across the North Sea, before the English battleships could get back from the Mediterranean, was a best-selling subject for the popular press, from 'Chums' to the Harmsworth journals.

Wodehouse's The Swoop is a short squib, taking off these invasion-scare writings as well as the recently formed, and popular, Boy Scouts. England is invaded by the armies of a multitude of enemies: Saxe-Pfennig, Russia, Afghanistan, China (under General Ping Pong Pang), Turkey, Morocco, Monaco and the distant isle of Bollygolla. England's defences crumble - it's August and everybody is away on holiday. Only the Boy Scouts resist the invaders. Clarence Chugwater, aged fourteen, and a junior reporter on an evening paper, is in command of a troop on the Aldwych site, and he leads his men in with catapults and hockey sticks. Eventually the music halls offer the invading generals and princes vast weekly salaries to appear nightly on their stages, Clarence himself topping the bills with £1,150 a week. Some real names occur. Edgar Wallace is a war correspondent, as he was at that time. Charles Frohmann is a theatrical producer, Baden Powell is head of the Scouts.

In 1915 Wodehouse adapted the book to signal an invasion of America by Germany and Japan in 1916, and sold it for serialization to the smart New York monthly magazine, Vanity Fair.

Source: Richard Usborne. Plum Sauce. A P G Wodehouse Companion.