The Blohm und Voss Bv 139 was the designation given to three four-engined flying boats produced as mail planes for Lufthansa, but that served with the Luftwaffe during the Second World War.
In 1935 Lufthansa issued a specification for a seaplane capable of serving on their trans-Atlantic mail routes. The new aircraft needed to have a cruising speed of 155.3mph, to be able to carry 1,102lb of cargo for 3,106 miles (5,000km), and to be strong enough to take-off and land on rough water or to be catapult launched.
Blohm und Voss responded with the Ha 139, a four-engined float-plane with inverted gull-wings. The floats were attached to the base of the 'V' on each wing, with the engines on the outer wing sections, carried on nacelles . Fuel was stored in the large-diameter steel tube used as a main wing spar. The main fuselage had a circular cross-section, and was of metal monocoque construction.
The first aircraft, Ha 139V1, made its maiden flight in the autumn of 1936, and during 1937 this and the V2 were used by Lufthansa on trials over the Atlantic, flying between New York and the Azores. These trials, which lasted until November, revealed some directional instability problems, and the original circular fins and rudders were replaced with larger versions. Better engine cooling was also required.
Trials resumed between July and October 1938, alongside trials on the third prototype, Ha 139 V3. This was a larger, heavier version of the aircraft, with the engines mounted lower on the wings.
All three aircraft were accepted by Lufthansa, and a regular trans-Atlantic mail service began, only to be interrupted by the outbreak of the Second World War. All three aircraft were soon taken over by the Luftwaffe. The first two were used as troop-transports in Norway, as the Ha 139A.
The third prototype had a more varied, if short, military career as the Ha 139B. It was originally converted to act as a reconnaissance aircraft, as the Ha 139V3/U1. In this version it had a longer glazed nose carrying an observer, and a larger vertical tail. Four 7.92mm machine guns were carried, one each in the tail, nose and two beam positions.
The V3 was modified again to act as a mine sweeper, this time as the Ha 139B/MS. Mine sweeping equipment was added, and the guns removed.
None of the three aircraft remained in service for long, soon being grounded by a lack of spares. Plans for a bomber version came to nothing, although a land plane based on the same design was built, as the Ha 142.