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Blohm & Voss BV 138 – The Sea Dragon: Germany’s Maritime Aviation Marvel

During the course of the Second World War, most of the combatant nations employed flying boats or seaplanes in a variety of roles. Besides air-sea rescue, flying boats were also used in the vital duty of maritime reconnaissance and patrol, where their ability to operate in any littoral or oceanic area was matched by their long range and loiter times.

Conception and Development

Responding to a Luftwaffe requirement proposal, the BV 138 was conceived in 1936, but developmental difficulties meant that the type did not enter service until 1940. Initially known as the HA 138, three prototypes were individually manufactured but work on the third was abandoned due to new design priorities.

The first two flew in July and August 1937 respectively, and the data gathered from these led to six pre-production models being manufactured, and these were known as the BV 138A version.

Despite some re-design work on these pre-production aircraft, the ‘A’ model was deemed unsatisfactory, and yet more design tweaks were introduced which led to the BV 138B-1, of which 21 examples were made.

Along with hull re-design work that eliminated aerodynamic and hydrodynamic failings encountered in the earlier models, the B-1 introduced new power plants, which were Junkers Jumo 205D diesel engines, rated at 880HP.

A cutaway of a Junkers Jumo 205 diesel engine. Three of these powered the BV 138.. Photo credit – Kogo GFDL.

The choice of diesel was made to enable the aircraft to refuel from tenders at sea, and even at times from U-boats in remote locations.

The BV 138 was an unusual and unique design concept, with a twin-boom tail unit, and three engines mounted above the wing. The unusual curved hull, which was employed because of hydrodynamic requirements led to the BV 138 being nicknamed ‘Der Fliegende Holzschuh’ (the flying clog).

Despite its unusual appearance and the problems encountered during the design gestation, the BV 138 matured into an excellent aircraft of its type, demonstrating high survivability, long-range and ability to operate in all types of weather.

The main production variant of the BV 138 was the C-1 model, of which 227 models were made until production ended in 1943. Entering service in March 1941, the C-1 introduced further improvements, with more powerful engines and standardised armament. The total number of all variants of the BV 138 numbered 297 examples manufactured during the conflict.

The BV 138 served in many areas in the European theatre of operations, and operated from coastal airfields and floating bases with seaplane tenders. Hard points were fitted to some examples to allow them to be catapulted from surface ships, and all models were equipped to employ launch boosters to help in marginal flying conditions.

The BV 138

The BV 138 was 20 metres (65 feet) in length, had a height of 6 metres (19 feet) and had a wingspan of 27 metres (88 feet). Empty, the aircraft weighed in at 11,770 kg (25,950 lbs) and the typical loaded weight was 14,500 kg (31,970 lbs) while the Max Take-Off Weight (MTOW) was 17,500 kg (38,590 lbs).

The crew consisted of 6 personnel; pilot, navigator, radio operator, nose gunner, rear gunner and upper rear gunner. When used in a transport role, the BV 138 could accommodate up to 10 passengers.

The C-1 variant introduced the penultimate power plant for this platform, which was an uprated Jumo 205D diesel producing up to 1000 hp. This model also introduced a new four-blade propeller for the centre engine.

The performance figures produced by three of these engines allowed the BV 138 to cruise at 200 km/h (124 mph) with a top speed of 285 km/h (177 mph). The aircraft had a service range of 4,300 km (2,670 mi) and could attain a ceiling of 5,000 metres (16,400 ft). The BV 138 had fuel tanks with a capacity of 825 Imperial gallons of diesel.

All flying boats of the Second World War were heavily armed to defend themselves against fighters and to engage their own type and surface targets when encountered on long patrols. The BV 138 was no exception to this rule and was very heavily armed indeed.

Two MG 151 20 mm cannon were carried, with one in a power turret on the hull nose, and the second in the rear fuselage firing aft. Additionally, a MG 131 machine gun of .51 calibre (13 mm) was fitted behind the central engine, and was used to cover the top rear of the aircraft.

Up to three MG 13 7.92 mm machine guns were employed by some crews in additional defensive firing positions. Racks on the inner wings allowed up to 600 kg of ordnance could be carried externally, and consisted of either bombs or depth charges.

The first combat employment of the BV 138 was in the invasion of Norway in April 1940, when several of the pre-production ‘A’ models were pressed into service as maritime transport aircraft. With the design flaws of the earlier models partially rectified with the introduction of the B-1 model in November 1940, the BV 138 served in small numbers until the introduction of the C-1 variant, the main production version in March 1941.

Large-scale deployment of the aircraft from 1941 onwards demonstrated the sterling qualities of the latest model, and the BV 138 enjoyed a good reputation with its crews, being appreciated for its toughness and endurance.

While not agile enough and too slow to combat fighters, its heavy defensive armament allowed it to sometimes hold its own in air combat, and the BV 138 was a deadly opponent for other maritime patrol and transport aircraft, with recorded air-to-air victories over the Blenheim bomber and the Catalina flying boat.

However, by late 1943 growing Allied air superiority saw increasingly heavy losses in combat, and as no replacement aircraft were available from this time, the efficiency and combat capability of squadrons equipped with this aircraft slowly declined from now until the end of the war in Europe.

The main areas where the BV 138 operated were the North Atlantic and Arctic Oceans, but the type also saw service in the Mediterranean, Baltic and Black Seas. Most aircraft of this type operated out of occupied Norway, being utilised to interdict Allied supply convoys heading for the USSR.

From bases in Norway, aircraft would patrol vast expanses of the North Atlantic, reporting convoy positions to waiting U-boat packs, and also engaging Allied cargo vessels with bombing attacks and cannon fire.

A particular duty performed by the BV 138 were attacks on Allied ASW aircraft such as the Catalina and Sunderland flying boats, in a concerted effort to provide some cover for U-boats.

However, operations like these were only feasible in the early part of the Battle of the Atlantic, when the air-sea gap uncovered by fighters during this time meant that the BV 138 and other long-range maritime aircraft like the Condor only had a limited period of success. From the middle of 1943, growing numbers of Allied escort carriers equipped with fighters effectively closed the air-sea gap, and German losses of maritime patrol aircraft began to mount.

The aircraft was also used to support German surface units on the rare occasions they sortied to interdict Allied supply convoys. In this type of operation, BV 138s were employed as long-range scouts for German heavy cruisers and pocket battleships, often rendezvousing with U-boats in remote stretches of both oceans to be refuelled with diesel from the U-boat’s bunkerage.

On one daring occasion in 1943 several BV 138 and their crews were operating from Novaya Zemlya in the Arctic Circle, flying out of a temporary airfield for nearly three weeks.

From late 1941 most aircraft were fitted with surface-search radar to better equip them for anti-shipping duties. One late development for the platform was the service entry of the BV 138MS, a specialised mine-sweeper variant.

Stripped of all its armament and equipped with a magnetic ring 14 metres in diameter, this model was equipped with an auxiliary generator to power the de-mining equipment. As the BV 138MS flew low over minefields, the energised ring generated enough power to detonate magnetic mines below the aircraft’s flight path.

With the war going against Germany, Norway was retained as a base until the end of the war, and several BV 138s operated from here until the cessation of hostilities in Europe.

The last recorded instance of the aircraft being used in combat was May 1st, 1945, when a BV 138 was ordered to fly to Berlin to remove Adolf Hitler’s will. Despite making a successful landing under artillery fire on Lake Berlin, the aircraft commander refused to allow the couriers to take the will, as they lacked formal identification papers. Instead, the aircraft was loaded with ten wounded soldiers and then safely departed for Copenhagen.