Originally developed under the company name of Hamburger Flugzeugbau, the type was initially designated the Ha 138. Its appearance was unique in its combination of unusual design features with its twin boom tail unit, short fuselage and trimotor engine configuration. The short hull, with its hydrodynamic step beneath and flat sides, earned it the nickname, "Fliegender Holzschuh". Three piston engines were used. The central engine was mounted above the wing, driving a four-blade propeller, while the wing engines were lower, with three-blade propellers. The pre-production prototypes and the BV 138 A-01 to BV 138 A-06, were powered by various makes of engines ranging from 485–746 kW. The first standardized version, BV 138 B-1, was powered by three 880 PS Junkers Jumo 205Dtwo-stroke, opposed-piston aircraft diesel engines. The engine cowlings also had an atypical appearance, due to the unique nature of the vertical orientation of the six-cylinder opposed-piston Jumo 205 diesel engines, and resembled the cowlings of 4 or 6-cylinder inverted inline engines found on smaller civil and utility aircraft from the Jumo 205's propshaft placement, emerging forward at the uppermost front end of the powerplant. The booms of the twin tail unit, much like the smaller Focke-Wulf Fw 189 twin-engined reconnaissance monoplane, extended horizontally from the rear of the outer engine nacelles. For hydrodynamic reasons, the hull featured a distinct "turn-down", or "beak" at the stern. Two enclosed, powered gun turrets, each mounting a single MG 151/20autocannon, were located prominently at the bow and stern. A third, fully open Scarff ring-like emplacement, behind the central engine and both above and forward of the rear turret, mounted a 13 mm MG 131heavy machine gun which covered fields of fire obstructed from the other turrets by the horizontal stabilizer.
Operational history
In all, 227 examples of standard service variants of the BV 138 were built. The first such variant, BV 138 C-1, began service in March 1941. While non-standard variants carried a variety of armament, the standard variant featured two 20 mmMG 151/20 cannon, one in a power-operated bow turret and one in a power-operated stern turret, up to three 7.92 mm MG 15 machine guns, and a 13 mm MG 131 machine gun in the aft center engine nacelle. It could carry up to 500 kg of bombs or depth charges or, in place of these, up to 10 passengers. Both the B-1/U1 and C-1/U1 variants had racks under both wings to double the offensive load. Some examples of the BV 138 were adapted to specialized roles. The Bv 138 was tested with the oft-used Walter HWK 109-500StarthilfeRATO jettisonable rocket pod, used in pairs, for shorter takeoff performance. One anti-shipping variant carried FuG 200 Hohentwiel low-UHF band maritime search radar. The BV 138 MS variant was converted for minesweeping, and carried magnetic field-generating degaussing equipment, including a hoop antenna with a diameter equal tothe length of the fuselage, which encircled the hull and wings, which was also used on certain models of the Ju 52/3m trimotor transport used for the same duty.
No complete BV 138s remain in existence. However, the wreck of one aircraft, sunk after the war in a British air show, was raised from the seabed of the ØresundSound in 2000, and is on display at the :da:Danmarks Tekniske Museum|Danish Technical Museum in Helsingør. On 27 June 2012, two divers found a Heinkel He 114 seaplane in Siutghiol Lake near Mamaia, Constanta, Romania. During that time, the two divers also found pieces of a Blohm & Voss BV 138 seaplane. In June 2013, a vessel from the Norwegian Geological Survey filmed a Blohm & Voss BV 138 at a depth of 35 m in Porsangerfjorden, Norway, not far from the WW2 German seaplane harbour in Indre Billefjord.
