Although the Martin Model 162 is better known as the PBM Mariner flying boat, its experimental antecedent was the Model 162A which was a three-eighths scale flying testbed of the PBM Mariner's hull and aerodynamic layout. Built from wood framing with aluminum skin, the Model 162A is believed to be the first subscale flying model built of a production aircraft in the United States. Due to its size and single pilot, it was nicknamed the "Tadpole Clipper" and began its flight tests in support of the PBM Mariner program in December 1937.
As there were no radial engines in existence that could fit the small scaled cowlings of the Tadpole Clipper, a single 120-horsepower four-cylinder inverted-vee piston engine inside the fuselage drove the twin props in the nacelles via drive belts. The Tadpole Clipper survived its flight test program and was restored by the Smithsonian Air & Space Museum and is on permanent loan and display in the Decker Gallery of the Baltimore Museum of Industry.
Source: Wings of Fame, Volume 7, Aerospace Publishing 1997. "Variant Briefing: Martin Flying Boats- Mariner, Mars, and Marlin Variants" by Robert F. Dorr, p122.