Bela Lugosi's illness prevented him from finishing the 1936 Republic feature A Casa das Mil Luzes (1936), so he completed his one-picture Republic contract with this 12-chapter serial, his only screen role during the full two year-horror ban.
CHAPTER TITLES: 1. Disaster At Sea; 2. Barrage Of Death; 3. The Gas Chamber; 4. The Fatal Shaft; 5. The Mystery Ship; 6. Deadly Cargo; 7. Undersea Terror; 8. The Crash; 9. Wolves At Bay; 10. The Acid Trail; 11. The Sea Battle; 12. The Deadly Circle.
In Chapter 10, a store can be seen by the name of "Weeks Books". At the time, Bela Lugosi had been previously married to Beatrice Weeks, whose late former husband was an architect who designed many buildings. It is unclear whether this was a coincidence or, since the building resembles a fake movie storefront, a thin-veiled reference done on purpose.
Filmed June 20-July 15 1937, released August 28. A feature version was issued in 1942.
William Witney and Maxine Doyle married after the making of this serial. They married about ten months later.