The battalion was given six months to clear the backlog, piled up in rat-infested warehouses in Birmingham. The rats feasted on the parcels of rotting homemade food.

In shifts lasting more than 24 hours, they sorted 17 million letters and packages in half the target time.

“Evelyn said the women were really enthusiastic to serve overseas and knew they were the select few to have this opportunity in combat theatre,” said Dr Hearn.

One of her outstanding memories was when the entire unit was sent to London to parade before Mary, the Queen Mother.

The film is in cinemas now and will stream on Netflix from 20 December.