A nitrate print of this film survives in the UCLA Film and Television Archives, and is not listed for preservation.
John mentions Jim was killed by a "variation of the Lewisite formula". Lewisite is an organic arsenic compound named after U.S. chemist Winford Lee Lewis (1878-1943) who "rediscovered" the compound in 1917 and envisioned its uses as a chemical warfare agent.
The airplane Becker boards at the beginning of the film is a 1936 Douglas DST-144 (DC-3) "Douglas Sleeper Transport", owned by American Airlines, registration NC16006. It was the seventh DC-3 built, and was named "Flagship Arizona". During WWII it was converted to a C-47, registration 42-56095. After the war it was returned to AA service. In the early 1950's it was sold to Brazilian airline Real and then to Sadia. On August 4, 1963 it crashed near Videira, Santa Catarina, Brazil while attempting to land in poor visibility killing all 10 on board.
Marian Hall 's debut.
U-186 is reported to Dr. Bremmer to be at Barnegat Light charging it's batteries. Barnegat Lighthouse is real and off the coast of New Jersey reinforcing the knowledge of that time that Nazi U-Boats were patrolling the waters off the United States. The Dr. asks for a radio message be sent to the U-Boat to pick him up at a specific location for his transport back to Germany..