Interview: Bernard Cornwell, author

Bernard Cornwell doesn't know how to be dull. In conversation, as on the page, he holds his audience with a seemingly effortless command of historical detail that's actually the product of painstaking research. Whether recounting the intricacies of a centuries-old battle, or gossiping about history's so-called heroes, Cornwell's gift is to make it sound as though he's reporting from the front lines.

With The Fort, he shatters popular misconceptions about the American rebels who fought in the Revolutionary War and the British troops who opposed them. It's the first time that his hero hasn't been fictional and, after 30 years in the US, he's also aware of the danger in choosing this subject matter. "When you're writing about the American Revolution you're trespassing on the high ground of American legend and myth, and you really can't take great liberties with it."

This is the story of the Penobscot Expedition of 1779, the worst naval disaster in US history before Pearl Harbor. Some 37 rebel ships were taken or burned at Penobscot. The American defeat is all the more embarrassing because rebel troops outnumbered the British - most of whom were Scots - and the British had just three small ships with limited firepower.

Penobscot, now in Maine, was still part of Massachusetts at the time. British troops had been sent to establish a province that would function as a naval base and as a sanctuary to loyalists.

The three British sloops-of-war blocked the entrance to Castine Harbor, while soldiers were sent ashore to establish a fort. Cornwell writes: "They did not know it, but the greatest naval force assembled by the rebellious Americans was on its way to 'captivate, kill or destroy them.'"

Captain Henry Mowat commanded the British sloops. His opposite number was Commodore Dudley Saltonstall, a man whose pomposity was boundless. Seeing the three ships blocking the harbour, he decided it was a fool's errand to try to sail past them, certain that once in, he'd never escape the harbour intact.

Instead, Saltonstall relied on the efforts of the thousand men commanded by Brigadier-General Solomon Lovell, and bolstered by the Massachusetts Artillery Regiment, led by Lieutenant-Colonel Paul Revere, plus an additional 220 rebel marines. It was expected they would storm the fort, whose construction was in its infancy.

On the British side, notables included 18-year-old Glaswegian Lieutenant John Moore, who "went on to revolutionise the British Army and (was] the man who forged the famed Light Division", and Francis McLean, a Scottish brigadier, who emerges as one of the novel's major heroes.

The other great hero - and who, alongside McLean, proved Cornwell's favourite to write - was Peleg Wadsworth, a lone voice of reason whose tactical suggestions are too often overlooked.

Saltonstall refused to sail into the harbour until Lovell captured the fort, and Lovell refused to capture the fort until Saltonstall sailed into the harbour. Lovell's reticence was ridiculous: when the Americans arrived, the fort's walls were no higher than a coffee table. But the canny Scots took advantage of rebel dithering and expanded the building daily.

Over tea and biscuits at London's Covent Garden hotel, Cornwell tells me: "One of the things I found curious is that the Scots are behaving as we're always told rebels behaved. There's no great aristocratic snob running them, and the men are sneaking off into the woods to ambush the Americans, against orders. Meanwhile, the Americans were led by this terrible snob, Saltonstall and by Lovell who doesn't dare move - he's a rabbit in the headlights.

"George Washington, strangely, believed an officer should be a gentleman and come from a good background - and this is not what we think about rebels. We think of them putting on the homespun and shooting from behind trees. Well, no."

Each chapter is introduced by extracts from contemporary historical documents. "One is a letter from the American militia which says, 'We've got a terrible problem, all our officers' commissions are signed by George III. We can't fight.' And I thought, 'You're rebels! Just go off and fight!' But no, they're worried, and the general court worries back, until they finally issue new commissions."

The novel's strong Scottish element is a fluke, he admits. "These just happened to be the regiments in the garrison at Halifax. The Hamiltons were a brand new regiment raised by the Duke as a patriotic gesture. He paid for everything. I don't think anyone looked around and said 'Let's send Scottish troops.' But it happens that the Royal Naval commander was a Scotsman, so this turns out to be a Scottish show.

"The Scots have got a wonderful reputation for soldiering anyway and Scottish regiments have great pride. What's equally amazing is out of those 700 men, the infantry, probably fewer than 30 or 40 had any experience of war. Both were fresh regiments.

"So you've got these 700 very young men, who were probably very frightened, who'd never really been in a battle. There's no doubt that McLean screws up the opening (of the campaign], and Moore definitely screws up, too. To lose a quarter of your men is not good. But they recover their balance, and once McLean has a measure of what he's up against, you can feel his confidence rising. As he says in a letter, 'Our chief difficulty lay in restraining our men.' You've got these Scots sneaking out to go to fight the Americans without permission. Behaving as we're told the rebels did behave. Well no, it was the other way around. But I think the Scots should be terribly proud of this expedition. Outnumbered, and they do everything right."

Conversely, the Americans couldn't have messed up more if they'd been ordered to throw the fight.

Another intriguing fact uncovered during nine years of research - begun out of curiosity, not with a novel in mind - was that British soldiers remained in, or returned to America to settle. And, surprisingly, they were welcomed. "Mowat died after the peace had been signed. He was the captain of a frigate and it was off the coast of Virginia, but he wasn't buried at sea, he was buried in the graveyard in Virginia. I have no idea why. It's a mystery. And there's a graveyard in Connecticut where there are seven British soldiers. The inscription says; 'In life our enemies, in death our guests.' It's sweet isn't it?

"At least six British soldiers of Penobscot returned after the war to settle. It suggests that the local population was still pretty loyalist. And they undoubtedly did settle there happily, because the obituaries in the local paper were very generous."

For this American expat, the most interesting discovery was that Paul Revere was such a despicable man, and far from the hero I grew up believing him to be. Thanks to Henry Longfellow, I believed Revere singlehandedly rode through the night warning, 'The British are coming!'"

Together, Cornwell and I recite: "Listen my children and you shall hear/ of the midnight ride of Paul Revere."

Utter nonsense, he says - and Longfellow knew it!

"Revere has been elevated so high in the pantheon (but] he was simply not famous in the 1850s. I think people in Boston knew that he had been a passionate patriot, but he was just one of many. Suddenly in 1861, the poem is published in The Atlantic Monthly, and he becomes this soaring hero. And Longfellow knew he was creating fiction. He knew that 30 honourable guys rode that night and that Revere did not reach Concord. Revere was captured. The Brits got hold of him and kept his horse and let Revere go. That's what stopped him reaching Concord.

"I'm not putting down Revere for the ride, and he'd undoubtedly been very active in the cause before the war. Longfellow was trying to write a great patriotic paean on the eve of the Civil War. He was trying to unite America, to bring it back to its revolutionary ideals, at a time when he saw it sliding into this horrific war. And it worked brilliantly! Suddenly Revere is this great, glowing hero."

At Penobscot, Revere is anything but. He defies authority at every opportunity - most shockingly when he refused to rescue the stranded crew of a schooner during the retreat. Revere insists that he's no longer beholden to his superiors, and won't risk losing his baggage to the British. He makes his way back to Boston, where he's placed under house arrest and eventually - at his own insistence - court-martialled.

"He picks a fight with everybody, and seems to have a chip on his shoulder. It's a class chip. He was twice refused for a Continental Army commission because he was not enough of a gentleman. He's a tradesman and didn't go to university. Now curiously, I think if Revere had been in Lovell's place, he'd have charged (the fort] and they'd have won. Because Revere was unreasonable enough, and you needed that. I think he resented being under command, because he thought he was better than they were. And there's this local legend that he stole the pay chest. I don't know if that's true but he certainly seems to be a great deal better off after the expedition than before."

The supreme irony, writes Cornwell, "is that Peleg Wadsworth, who promised to have Paul Revere arrested and who was undoubtedly angered by Revere's behaviour … was the maternal grandfather of Henry Wadsworth Longfellow … Peleg Wadsworth would have been appalled, but as he surely knew better than most men, history is a fickle muse and fame her unfair offspring."

• The Fort is published by HarperCollins, priced 18.99