From Julius Caesar to Adolf Hitler, the invasion of Britain has been a constant theme in the history of these islands, even if the successful attempts have been heavily outnumbered by the unsuccessful ones.

Until now, however, one plan has remained unknown: an 18th-century plot to invade with an American army during that country’s War of Independence.

Drawn up by a French general, the scheme was to bring over an American force of 10,000 that would find a Britain so distracted by the war on the other side of the Atlantic, that victory would seem certain. Just to make sure, however, the general suggested that the force include a corps of Native Americans, or “sauvages”, as he termed them, who would strike such fear in British troops that any resistance would collapse immediately.

The plan, which is being sold at auctioneers Bonhams in London next week as part of a lot of books, was drawn up by Charles-François Dumouriez when commander at Cherbourg. The document, which bears a pencil note saying it came from the papers of General Barthélemy Scherer, briefly Minister of War, says it would be easy to take the Americans across the Atlantic, and suggests if they landed in Ireland “they would be guaranteed success”.

With a corps of just 500 Native Americans, right, the document notes: “It is impossible to imagine the terror that would strike the British on seeing them”.

The scheme, which is sufficiently detailed to include discussion on the likely deployment of British forces, and the supplies, ships, horses and artillery needed, also considers what would happen if there were a shortage of Native Americans: “Even if the Bostonians could not assemble this number of savages, they could dress up and paint themselves,” it says. “These phantoms would be enough, by their mere appearance, to cause mass desertions amongst the British.”

It is not known how the Americans reacted to the proposal — if they ever knew.

In 1779 a Franco-Spanish attempt was mounted to invade the Isle of Wight, taking advantage of the British fleet spread between America and the West Indies, but the force was blown off course. Jeremy Black, a professor of history at Exeter University, said: “It is fantastical, in terms of the technology but ... completely mad — there is no way they could have made it across the Atlantic.

Projet d’une Descente en Angleterre pour l’Année 1779 is part of a sale of books on October 6.

We’ve been here before

• Operation Sealion was Germany’s plan to invade Britain in early 1940. Hitler knew that, with a small German Navy, he needed air supremacy to succeed. After losing the Battle of Britain, the plan was put on hold.

• The Battle of Fishguard is often called the “last invasion of Britain”. On February 22, 1797, 1,400 French revolutionary troops landed at Carregwastad Head in Wales. Several skirmishes with disgruntled locals triggered widespread desertion from the French and the “army” surrendered after only two days.

• In 1066 William the Conqueror led his Normans across the English Channel to fight King Harold at the Battle of Hastings. On August 14 Harold was killed and the Anglo-Saxons fled.

• In 865 the Vikings attacked East Anglia and marched north, making York their capital. The ensuing centuries marked many battles for the North East between the Danes, Norwegians, English and Scots.

• The Romans tried several invasions of Britain, the first under Julius Caesar in about 55BC which really only gained a beachhead in Kent, but they succeeded more meaningfully in AD43 and stayed until the 5th century.

Explore UK News

• Crime News

• Education News

• Health News

• Scotland News

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads