The model submarine Nautilus used in filming was originally built as one of the "SEAVIEW" filming models (eight feet long) for the 1960 movie "Voyage to the Bottom of the Sea", also created/written/directed/produced by Irwin Allen. Many Hollywood prop collectors bemoan the conversion of the SEAVIEW for use in this very short lived TV show. The model has probably been destroyed at this point.
The villain's submarine was modified from a Space:1999 Eagle play-set. The toy was made by Mattel in 1976, two years before the film. The engine section, side cargo doors, command capsule, and framework superstructure from the Eagle are all visible on the modified submarine.