They encountered a Japanese fishing vessel which they had to take out, and couldn't be sure that they'd not been 'made'. So they had to launch early, making it difficult at best to reach a safe landing area.
They all knew it, and they all took off anyway.
"John Birch was a courageous Baptist missionary who went to China in 1940. When Colonel Jimmy Doolittle led the famous World War II bombing raid on Tokyo, John was brought to the survivors and he helped them to safety, then volunteered, creating an intelligence network that saved countless American lives.
He earned the rank of Captain in the 14th Air Force, as well as numerous commendations, including the Legion of Merit. Ten days after the war officially ended, Captain Birch was brutally killed by Chinese Communists. "
Great stuff!
Eventually, they ended up under house arrest near the Iranian border. They "escaped" to walk across the border into Iran.
