Seven Years%27 War
The troops were reembarked and moved to the Bay of St. Lunaire in Brittany where, on 3 September, they were landed to operate against St. Malo; however, this action proved impractical. Worsening weather forced the two armies to separate: the ships sailed for the safer anchorage of St. Cast, while the army proceeded overland. The tardiness of Bligh in moving his forces allowed a French force of 10,000 from Brest to catch up with him and open fire on the reembarkation troops. A rear-guard of 1,400 under General Dury held off the French while the rest of the army embarked. They could not be saved; 750, including Dury, were killed and the rest captured.

Q: What happened to the British army?
a French force of 10,000 from Brest to catch up with him and open fire on the reembarkation troops