From his collection stored in the "Hidalgo Trading Company" warehouse Doc uses a fast, silenced Motorboat, capable of self-righting itself after capsizing with a pop-up gun and tripod. The boat is described as being considered by the navy for the basis of "a fleet of light coastal defense speedsters" (similar to an armed Motor life boat in description). Last, and also from the warehouse, Doc again uses the "Helldiver" submarine (first seen in "The Polar Treasure", June 1933). The "Helldiver" has many gadgets and experimental devices built into it. In this story the principle modifications are a mechanism to release a chemical similar to squid ink, external-viewing television screens and dial-based sonic devices allowing it to successfully navigate through New York harbor, and its traffic, while submerged.