Spoilers ahead for the most recent episode of Outlander.
At just under 15 minutes, the Battle of Prestonpans may actually be one of the shortest battles in history. While that might make it easier in some ways to adapt for television, the reason the battle was brief is also what made it so challenging to shoot for the latest episode of Outlander.
"The way the battle was won and was over so quickly was because it was so foggy," locations manager Hugh Gourlay explained. "The battle itself was fought in the mist," Outlander's U.K. producer David Brown added. "There was a sea mist coming off because the battle site was down near Edinburgh."
The early morning mist helped obscure the Highlanders' surprise attack — their advance guard was able to sneak up on British soldiers by circling around their lines, coming out on the other side to hit the opposition's unprotected left flank. This was key, since the Jacobites couldn't match the British in arms, having mostly blade weapons, farm tools, and only a few guns, while the British had cavalry and artillery. But by charging at them unawares, the Jacobites prevented the British from using some of those weapons, at least more than once.
The Outlander team wanted to be historically accurate, especially when it came to the mist. But how, and still have workable shooting conditions?
First, they tried artificial smoke, thinking it could be augmented by special effects. They found a field at the edge of some woods that matched the original battle site and did a smoke test to see how it might work. "It was a disaster," laughed Brown. "The smoke went everywhere except where we wanted it to! It was too weather dependent. So the question was, what are we going to do? This is a big number for us, and it has to work."
Since they couldn't contain the smoke outside, they thought they might have to shoot inside. A built filming stage, however, was out of the question — they needed actual terrain, with a large enough run for cavalry horses to gallop. So they explored the idea of using an indoor riding school, but that didn't account for the woods, which the soldiers needed to emerge from. The solution was a little bit of both: shooting inside and outside at the same time. "We decided there would have to be white clouding all around, and somebody said, 'Why don't we do it under a marquee tent, because it's already white?'" Gourlay said.
Just down the road from their production stages at Cumbernauld, they found another field and covered it with an enormous, white marquee tent and filled it with a smoky mist. This way, they could control how much or how little they wanted, without any wind interference.
The actors were surprised to find out that this was how they were going to shoot the scene, but delighted by the prospect. "I've never done anything like that before," said Graham McTavish, who plays Dougal. "My God, it was bigger than a football field. I cannot imagine what they would ever use that tent for in the normal run of things. You'd have to have the biggest wedding in the world!"
Inside the tent, it was difficult for the actors to maneuver. They were at least a foot deep in the mud, said Stephen Walters, who plays Angus. In order to have any grip on the ground, they needed metal-plate crampons attached to their shoes. Plus, they could hardly see around them. "The look, the sound, everything was different," McTavish said. "You could just see through the depth of the fog a bit, for the foreground battle sequence, but then you'd just barely be able to see horses rearing in the background through the mist."
Using the mist had one benefit: it helped obscure how many extras Outlander used to recreate the battle — the British and the Jacobites had over 2,000 men on each side, but the show wanted to use no more than 120 for each army.
By the end, they felt they’d re-created the battle — which plays out in almost real time in the episode — as accurately as they could. "And the audience will never know it was shot in a tent," Brown said. Well, until now.