Tupolev ANT-25 was designed specifically for setting flight range records. In 1937 two flights from Moscow, Soviet Union to USA via the North Pole happened - one covered 9130 kilometers and finished in Vancouver, Washington and another covered 11500 kilometers and finished near San Jacinto, California.
ANT-25 had a single V-12 piston engine. This sounds kinda not very redundant - should a single engine fail while the plane was crossing Arctic there was good chance the flight would end there and maybe the crew would not be rescued because simply reaching there would be problematic.
Why was a single engine airplane selected for this specific task where reliability was very important?