Trapped at Dunkirk

[kingston_123]

At the the beginning of the Dunkirk (2017) movie, this line was appeared:

The Enemy have driven the British and French Armies to the sea. Trapped at Dunkirk, they Await their fate.

who got trapped at Dunkirk?
There is a "subject" is missing in this sentence.

 

[Raymott]

It's ambiguous. But the subject is "they".

 

[kingston_123]

Who is "they" then?

 

[Raymott]

Who is "they" then?

Do you know the meaning of 'ambiguous'? It's a good word to know; we use it here a lot. As Piscean has pointed out, it means that the sentence structure doesn't say who 'they' is, and that you have to work it out from contextual material.