Jim Martin contracted Jensen to design and built him a glider for contest flying just before the Second World War. Jensen completed the aircraft in 1939.
The aircraft was constructed with a wooden structure and covered in doped aircraft fabric covering. The cantilever gull-style wing employed a NACA 4400 series airfoil. The tail was a conventional low-tail design and featured strut-bracing. The M-1 was registered as an Experimental - Amateur-built aircraft and was not type certified.
Martin flew the aircraft in a number of US Nationals, as did a later owner of the M-1, Emil Lehecka. While Lehecka owned it the aircraft picked up the nickname of the Whatsit. By the 1970s the aircraft was owned by Francis Kalinowsky and was based at the Circle X airport in Florida. At that time it was reportedly in good repair and was well maintained.
The aircraft was removed from the Federal Aviation Administration registry and its whereabouts are unknown.