There's another side to the story that gets told less often.

While all the battles were unfolding over there in North America, American revolutionaries were also working here in Britain to destabilise this nation.

(suspenseful music) The Royal Dockyard at Portsmouth was the main naval depot for the British, during the American Revolution.

And it was right here, in December 1776, that an act of arson set the docks ablaze.

(flames roar) I'd like to dig in to the detail of this attack, to find out if it was an American inside job.

I'm descending to the gun deck of HMS Warrior, to meet a terrorism expert.

James: So, got a wonderful description here from one of the investigators.

He's brought with him trial documents, including a confession, that reveal exactly how this attack was carried out, and by whom.

James, can you tell me about this bomb?

How did it work?

What did it do?

-The bomb was quite ingenious for its time.

So, this is a document from the prosecution.

-Wow.

The most ingenious bit is this in the middle here, a candle.

So, it's a timed wick.

It's not just what we call today, an improvised incendiary device, an IID.

It's a timed IID.

A candle would've been slowly moving towards the zero hour, and then (explosion).

-Very ominous.

-Gosh.

That sounds quite effective, then, it really worked.

How much damage did it cause?

Here in Portsmouth, pretty substantial damage, he gutted an entire building.

Wow.

I guess that the people in charge of the navy must have felt immensely vulnerable?

Very, it was a panic.

I mean, we're talking about a spate of attacks at key ports in the space of a couple of weeks.

The navy's being used to run fresh troops and munitions across the Atlantic, and that's the vital point here, is that it is the literal lifeline for the Crown forces over there.

Sounds like the work of a cell to me.

Well, that was the assumption.

The second these fires start, they believe there's a team of saboteurs at work.

And that they are indeed American-backed.

Turns out that it is just one man, and that comes across in his testimony when he's put on trial, that he has no accomplices.

He sounds like a proper criminal mastermind, doesn't he?

Well, he is and he isn't.

Contrary to the rumour at the time, he was not American, he was Scottish.

He went by the name of John the Painter.

-Ah... -His real name was James Aitken.

His plan was to attack the Royal Navy at a pretty sensitive time in the war, when the Royal Navy has commenced a blockade.

Lucy: Was he recruited by the Americans to help their cause, then?

He claims that he was there in Boston in December of 1773 to see the Tea Party, perhaps even participate in it.

And on that basis, he claims that he was radicalised.

He's not officially American, but he's definitely acting in American interests, isn't he?

Oh, very much so, I mean he really thinks that he is a fighter for the cause.