This Polish heavy bomber started out as an airliner. Prototype first flew March 1936 with two Pratt and Whitney Wasp Junior radials of 400 hp. Despite poor performance {212 mph top speed} and many problems the type was ordered into production. An evaluation team from Romania was killed when a Zubr broke up in mid-air, and the landing gear was so unreliable it had to be bolted down. When 16 were delivered in 1939, they were sent to an airfield that was bombed during early German attacks. They saw no combat being unable to take off.