The world of Song of the SlumdI is the same as the world of Worldshaker and Liberator, so it divides off from real history at the same moment, that is, Napoleon's tunnel under the English Channel. In real history, it never went past the planning stage; in my history, Napoleon actually had it dug - and history was changed from then pn.
The French engineer who came up with the idea was called Albert Mathieu-Favier. His plan was for a peacetime tunnel, and Napoleon toyed with the idea during a short period of peace. But when war loomed again, the idea was forgotten. Why? Napoleon ought to have seen the military potential - a way of crossing the Channel without having to confront the British navy.
In steampunk history, Napoleon did see the military potential, did have the tunnel dug, did invade England--and that's my point of departure for a hundred and fifty years of alternative history. But for this page, we'll stick to real history …
Napoleon being napoleonic
After the Battle of Marengo and the Battle of Hohenlinden, the continental powers of Europe made peace with France. Britain fought on for a while, but finally signed the Peace of Amiens in 1802. This was when Albert Mathieu-Favier approached Napoleon with his plan for a tunnel under the English Channel.
Mathieu-Favier was a French engineer and he’d developed his plan many years before. He hoped that Napoleon would give it backing as a means of communication and trade under the Channel (or La Manche, from the French side).
His idea was to dig a tunnel big enough for horses and carriages to drive through. Oil lamps would provide illumination, great chimneys rising above the sea would provide ventilation. The most ingenious part was the plan to use a mid-Channel sandbank, called Varne Bank, and built it up into an artificial island. Here the tunnel would emerge above sea-level, with a halfway staging post for changing horses.
Here’s a picture of an underwater section and one of the great chimneys.
Napoleon’s interest faded when tension between Britain and France built up again. Intending to invade, he created a huge military camp bear Boulogne, on the south side of the Channel. He didn’t actually think of the tunnel as a means of invasion—but he could have done!
In fact, he tried to concentrate the French and Spanish naval fleets, which together might hope to take control of the Channel. Instead, Nelson defeated them at the Battle of Trafalgar.
Napoleon broke up his Boulogne camp and marched against the Austria and Russia, which had joined Britain in a new anti-French coalition.
He crushed the Austrians at Ulm and Austerlitz, and soon had continental Europe at his feet again. But he never did get to invade England.