The Blohm & Voss BV 138 was one of those aircraft that looked odd at first glance but made deep operational sense once you understood what it was built to do.
A trimotor flying boat with twin tail booms, a short, “clog‑like” hull and heavy defensive armament, it became the Luftwaffe’s primary long‑range maritime patrol and naval reconnaissance flying boat over the North Sea, Arctic and Atlantic during the Second World War.
Origins and development
From shipyard to seaplanes
Blohm & Voss diversification:
In the early 1930s, the Hamburg shipbuilding firm Blohm & Voss was hit hard by the Great Depression and a slump in naval orders.
To survive, the company created an aviation subsidiary, Hamburger Flugzeugbau (HFB), in 1933, initially building components for other manufacturers such as Junkers before moving into its own designs.
Recruiting Richard Vogt:
Dissatisfied with early in‑house designs, the Blohm brothers recruited Dr Richard Vogt, who had been working in Japan for Kawasaki and had a reputation for unconventional but highly engineered structural concepts.
With seaplane specialist Hans Amtmann joining from Junkers, the firm quickly focused on flying boats and long‑range seaplanes, including the Ha 139 mailplane.
The Ha 138 requirement
RLM need for a long‑range patrol boat:
The Reichsluftfahrtministerium (RLM) sought a compact, long‑range maritime reconnaissance flying boat capable of operating from open water, supporting naval operations, and patrolling distant sea lanes.
Hamburger Flugzeugbau responded with the Ha 138, a relatively small but long‑legged flying boat that embodied Vogt’s taste for structural and layout experimentation.
From the twin‑engine concept to the trimotor:
The original Ha 138 concept used two diesel engines, but development problems with the powerplants and concerns about power margins for a heavily loaded flying boat led to a redesign as a trimotor.
The third engine, mounted in a central nacelle above the wing, gave better take‑off performance, improved safety over cold seas, and allowed the aircraft to carry more fuel and equipment without becoming dangerously underpowered.
Blohm & Voss BV 138A prototype
Prototypes and redesigns
First flight and early issues:
The first prototype, Ha 138 V1 (D‑ARAK), flew on 15 July 1937.
Flight and water trials quickly revealed hydrodynamic and aerodynamic shortcomings: the short hull pounded heavily in waves, and the twin tail booms and tailplane arrangement produced stability and control issues.
Hull and tail boom revisions:
Vogt’s team reworked the hull lines to improve planing and spray control and modified the tail booms and tailplane to cure directional and longitudinal instabilities.
These changes were substantial enough that development stretched over several prototypes and pre‑series machines before a satisfactory configuration emerged.
Transition to Blohm & Voss and production
Renaming to BV 138:
To reduce confusion between the shipyard and its aviation arm, the company’s aircraft were re‑coded from “Ha” to “BV” (for Blohm & Voss).
The Ha 138 thus became the BV 138.
Entry into service:
The first production‑standard BV 138A‑1 flew in April 1940, by which time Germany was already at war with multiple neighbours.
Operational introduction followed in late 1940, with the type quickly assigned to long‑range maritime reconnaissance units.
The definitive BV 138C‑1 entered service in March 1941. In total, about 297 BV 138s were built between 1938 and 1943.
Airframe and structural design
Overall configuration
Flying boat hull: The BV 138 was a true flying boat rather than a floatplane.
Its fuselage was a short, deep hull with a single step, designed to plane quickly onto the water’s surface during take‑off.
In side view, the hull’s profile resembled a wooden clog, earning the aircraft the nickname “Der fliegende Holzschuh” (“the flying clog”).
High wing and twin tail booms:
A high‑mounted, thick‑section wing spanned the hull, with two substantial tail booms extending aft from the wing to carry a high tailplane and twin fins and rudders.
This arrangement kept the tail surfaces clear of spray and allowed a compact hull while still providing adequate tail volume and control authority.
Materials and construction
Mixed construction:
The BV 138 used primarily all‑metal construction, with stressed‑skin techniques typical of late‑1930s German aircraft.
The hull was built from metal frames and skin, designed to withstand repeated water impacts and rough‑sea operations.
Internal watertight compartments provided buoyancy and damage tolerance.
Wing and booms:
The wing was a multi‑spar, all‑metal structure with integral fuel tanks.
The tail booms were metal box structures extending from the wing’s rear region, carrying the tailplane and fins.
The twin‑fin layout improved directional stability and gave a wide field of fire for the rear turret.
Hydrodynamic features
Step and spray control:
The hull incorporated a pronounced step to break water adhesion during take‑off, reducing drag as the aircraft accelerated.
Spray rails and chines along the hull sides helped deflect water away from the propellers and wing roots, improving visibility and reducing corrosion and impact damage.
Stability on water:
Wingtip floats were mounted outboard to provide lateral stability on the water.
The relatively short hull made the aircraft compact and manoeuvrable in harbours and coves, though it demanded careful piloting in heavy seas.
Propulsion, systems, and performance
Engines and propellers
Trimotor layout: The BV 138 was powered by three Junkers Jumo diesel engines (Jumo 205 variants), each driving a three‑bladed propeller.
Two engines were mounted in nacelles on the wing’s leading edge, and the third sat in a central nacelle above the wing.
The diesel engines offered good fuel economy and reduced fire risk compared to gasoline engines—valuable traits for long overwater patrols.
Engine advantages and challenges:
The Jumo diesels gave the BV 138 respectable range and endurance, but they were mechanically complex and required careful maintenance.
The central engine’s position also complicated access and slightly increased drag, yet the redundancy of three engines was reassuring for crews operating far from land in cold northern waters.
Fuel, range, and endurance
Long‑range patrol capability:
With fuel stored in the wing and additional tanks as needed, the BV 138 could remain airborne for many hours, performing extended patrols over the North Sea, Norwegian Sea, and Arctic approaches.
Exact figures varied by variant and load, but the type was designed around long endurance rather than high speed.
Operational radius:
In practice, BV 138s could patrol hundreds of kilometres from base, loiter in search areas, and still return with reserves.
This made them valuable for convoy shadowing, U‑boat support, and general maritime reconnaissance, especially in regions where land‑based airfields were scarce.
Flight performance
Speed and altitude:
The BV 138 was not fast.
Its maximum speed was modest for the era, and its cruising speed was lower still, reflecting its patrol role.
Service ceiling was adequate for maritime work but not high by land‑based bomber standards.
The aircraft relied on defensive armament and ruggedness rather than speed to survive encounters.
Handling characteristics:
Pilots reported that the BV 138 was solid but heavy on the controls, especially when fully loaded.
Take‑off runs on water could be long in calm conditions, though the trimotor power and hull step helped.
Once airborne, it was stable and suited to long, steady patrols rather than aggressive manoeuvring.
Crew, layout, and equipment
Crew complement and stations
Typical crew:
A BV 138 usually carried a crew of around six: a pilot, co‑pilot, navigator, radio operator, and one or more gunners/observers.
On some missions, additional specialists or passengers could be carried in the hull.
Internal arrangement:
The cockpit sat high in the forward hull, giving good visibility over the bow and to the sides.
Behind the cockpit were navigation and radio positions, with access to the bow turret and the central hull compartment.
Aft, the hull and wing roots housed ammunition, equipment, and sometimes extra seating or cargo space.
Avionics and mission equipment
Navigation and communications:
Standard equipment included radio sets for communication with ground stations, ships, and other aircraft, as well as navigation instruments suited to over-water flight: compasses, drift sights, and later, more advanced aids as they became available.
Radar and special gear:
Later BV 138s, particularly specialised variants, carried the FuG 200 Hohentwiel maritime search radar in a nose or dorsal installation, allowing them to detect ships and, to a limited extent, surfaced submarines in poor visibility or at night.
Minesweeper variants carried degaussing equipment and a large loop antenna encircling the hull and wings to generate a magnetic field for detonating magnetic mines.
Armament and defensive concept
Fixed and turret armament
Standard defensive fit:
The main service variant, the BV 138C‑1, typically carried two 20 mm MG 151/20 cannon in power‑operated turrets—one in the bow and one in the stern—plus up to three 7.92 mm MG 15 machine guns and a 13 mm MG 131 machine gun in the aft centre engine nacelle.
Fields of fire: The bow turret covered the forward hemisphere and some lateral arcs, while the stern turret and dorsal guns covered the rear and upper approaches.
The twin‑fin tail and high tailplane gave the rear turret a relatively unobstructed field of fire, making stern attacks hazardous for enemy fighters.
Offensive load
Bombs and depth charges:
The BV 138 could carry up to about 500 kg of bombs or depth charges, typically under the starboard wing root on standard variants.
Some sub‑variants added racks under both wings, doubling the offensive load for anti‑shipping or anti‑submarine missions.
Transport capability:
In place of external ordnance, the aircraft could carry up to around ten passengers or equivalent cargo, allowing it to serve as a small transport or liaison flying boat when needed.
Variants and experimental versions
Early and main production variants
BV 138A‑1: The A‑1 was the first production standard, entering service in 1940.
It embodied the major structural and hydrodynamic fixes developed during the prototype phase but was still something of an early‑batch configuration, with details later refined.
BV 138B series: The B‑series introduced improvements in equipment and detail changes, including armament and internal arrangements.
Some B-1/U1 aircraft were fitted with additional underwing racks to increase bomb or depth charge capacity.
BV 138C‑1 (definitive version): The C‑1 became the definitive and most numerous variant, entering service in March 1941.
It featured strengthened structure, refined armament layout, and updated equipment.
Most surviving photographs and accounts of BV 138 operations refer to C‑1 aircraft.
Specialized variants
BV 138 MS minesweeper:
The BV 138 MS was a minesweeper conversion, fitted with a large degaussing loop encircling the hull and wings.
By generating a strong magnetic field, it could trigger magnetic naval mines at a safe distance, clearing channels for shipping.
Similar equipment was used on some Ju 52/3m transports.
Radar‑equipped anti‑shipping versions:
Some BV 138s carried the FuG 200 Hohentwiel radar for anti‑shipping reconnaissance, enabling them to locate convoys and individual ships beyond visual range and in poor weather.
These aircraft acted as eyes for surface forces and U‑boats, relaying contact reports and shadowing targets.
RATO‑assisted take‑off tests:
The type was tested with Walter HWK 109‑500 Starthilfe rocket‑assisted take‑off (RATO) pods, mounted in pairs.
These jettisonable rockets shortened take‑off runs when heavily loaded or operating from restricted or rough water, though they did not become universal equipment.
Blohm & Voss BV 138A
Operational history and WWII context
Strategic role in the Luftwaffe
Primary maritime patrol flying boat:
Within the Luftwaffe, the BV 138 filled the niche of a long‑range maritime patrol and reconnaissance flying boat, complementing land‑based aircraft such as the Fw 200 Condor and Do 217 in over‑water roles.
It was particularly important in northern theatres, where bases were sparse and sea conditions harsh.
Theatres of operation:
BV 138s operated over the North Sea, Norwegian Sea, Barents Sea, and parts of the Atlantic, as well as in some other coastal regions.
They supported naval operations off Norway, monitored Allied convoys to and from the UK and the Soviet Union, and provided reconnaissance for Kriegsmarine surface units and U‑boats.
Blohm & Voss BV 138C
Missions and tasks
Convoy shadowing and reconnaissance:
A typical mission involved taking off from a coastal base, climbing to patrol altitude, and sweeping assigned sectors for shipping.
Once a convoy was located, the BV 138 would shadow it, reporting position, course, and speed, and sometimes directing U‑boats or strike aircraft to the target.
Anti‑submarine and anti‑shipping work:
Armed with depth charges or bombs, BV 138s could attack submarines spotted on the surface or just submerging and occasionally attacked small ships or coastal targets.
Radar‑equipped examples improved the Luftwaffe’s ability to find targets in poor visibility, though their offensive load was modest compared to dedicated bombers.
Minesweeping and special duties:
Minesweeper variants flew low over suspected minefields, using their magnetic loops to detonate mines.
Other aircraft were used for transport, liaison, and special missions, including inserting or extracting personnel from remote coastal locations.
Blohm & Voss BV 138C
Combat experience and survivability
Encounters with Allied fighters:
Despite its ungainly appearance, the BV 138 proved surprisingly tough.
Over Norway and the North Sea, early Allied carrier fighters such as Sea Hurricanes sometimes struggled to shoot down the heavily armed and rugged flying boat, especially when it could use its turrets effectively and hug low altitudes over the sea.
Vulnerabilities:
As the war progressed and Allied fighter coverage improved, the BV 138’s low speed and relatively limited manoeuvrability became more dangerous liabilities.
Losses increased when aircraft were caught without escort or forced to operate near heavily defended areas.
Nevertheless, its defensive armament and sturdy construction gave crews a fighting chance.
Blohm & Voss BV 138C
Operational limitations
Weather and sea state:
Operating from northern waters meant frequent encounters with poor weather, icing, and rough seas.
Take‑offs and landings in heavy swell were hazardous, and the short hull, while compact, demanded skill to avoid damage.
Maintenance in exposed coastal bases was also challenging, especially for the complex diesel engines.
Logistical and production constraints:
Only 297 BV 138s were built, a relatively small number compared to many land‑based types.
Production competed with other Blohm & Voss projects and with the broader demands of the German war economy.
This limited the scale at which the type could influence the maritime war, even though it was central within its niche.
Blohm & Voss BV 138C
Assessment and legacy
Technical and operational evaluation
Strengths: The BV 138 combined long endurance, good over‑water safety (thanks to three engines and a robust hull), and heavy defensive armament in a compact flying boat.
Its ability to operate from remote coastal bases and rough anchorages made it well suited to the northern maritime theatre.
Radar‑equipped and minesweeper variants showed how adaptable the basic airframe was.
Weaknesses: Its low speed, modest offensive payload, and relatively small production run limited its strategic impact.
The diesel engines, while efficient, were maintenance‑intensive, and the aircraft’s unusual configuration made some servicing tasks awkward.
As Allied air superiority grew, the BV 138’s survivability depended increasingly on careful mission planning and operating in less contested areas.
Blohm & Voss BV 138C
Place in WWII aviation history
Within the German seaplane family:
Alongside larger flying boats like the Blohm & Voss BV 222 and Dornier Do 24, the BV 138 represented the German commitment to maritime aviation tailored to specific theatres.
It was not a glamorous aircraft, but it was a workhorse that quietly underpinned reconnaissance and naval support operations in some of the war’s harshest environments.
Post‑war fate:
No large‑scale post‑war use of the BV 138 emerged; surviving airframes were scrapped or studied briefly by the Allies.
Unlike some contemporaries, it did not spawn a direct civilian or foreign military successor.
Its legacy lies mainly in its role as a specialised, highly distinctive maritime patrol flying boat that reflected both the ingenuity and the constraints of German wartime aircraft design.
