Development began in 1920 with the Do C III (Komet I). This was a high-wing commercial transport with an open cockpit for the pilot and an enclosed cabin seating four passengers. It had an exceptionally long wingspan of 17 m (55 ft 9.25 in) and could be powered by either a 180-hp BMW III or 185-hp BMW IIIa engine. It was built in small numbers and used by various German airlines with some success.

Designed in 1920 a modified version, the Komet II, utilized the same wing configuration, but with an increased overall length. The Komet II was a five-seat (pilot in open cockpit and four passengers in cabin) monoplane with a thick wing placed on top of the deep box-section fuselage. Powered by a 134kW / 250-hp BMW IV engine, it made its first flight on October 9, 1922.


A small number were built with 250 hp BMW IV engines and were operated from 1922 by Deutsche Luft-Reederei, and Rolls-Royce Falcon-engined examples went to Spain, Colombia, Russia and the Ukraine.


This was followed by the six-passenger Komet III, which first flew on December 7, 1924, with a 360-hp Rolls-Royce Eagle powerplant. This same engine was used in a parasol-wing development, the Do C, produced shortly afterwards as a training aircraft. Some Do Cs were operated by the Fuerza Aerea de Chile as light bombers in about 1930.

The Do D torpedo-bomber, which flew for the first time in July 1926, was a twin-float version of the Do C, with a 600-hp BMW VI engine, which entered limited production for the Yugoslav naval air service in 1927. In 1925, two other versions of the Kornet III were evolved: an ambulance model, desig-nated Do T, and a passenger counterpart with a 600-hp BMW VI, the latter receiving the name Merkur or DO B.

The final development of the Komet type was the Do.B Merkur, which first flew in February 1925 and was produced from 1926 as an eight-ten passenger airliner powered by a BMW VI engine. It could cruise at 175km/h. Following long-distance overland trial flights, dual controls and adjustable pilot seats were fitted. Deutsche Luft-Hansa received the greatest number with nearly 30 aircraft and these operated from Berlin to Konigsberg and elsewhere. Examples were operated by Deutscher Aero Lloyd and DDL in Europe, were exported to the Ukraine and licence-built in Japan and perhaps Switzerland in civil/military guises.


The Komet III used three different kind of powerplants. Some of them employed the Rolls-Royce 360 horsepower Eagles, others used the Napier 465 horsepower Lions, and the third powerplant was the 400 horsepower Liberty engine.

A twin-float seaplane version was also produced and Chile received a number as Do G trainers/torpedo-bombers. The Do D was similar to the Do C built for the Yugoslav Naval Air Service, while the Do T was an ambulance derivative of the Merkur.

A Pioneering Flight from Zurich to Cape Town in 1926
On 7 December 1926 the Swiss aviation Pioneer Water Mittelholzer embarked on a flight that would take him from Switzerland across the African continent to Cape Town in 77 days. It was the first crossing of Africa in a seaplane ever and became a landmark in Swiss aviation. But this flight was not about breaking another record. It was about adding the the very poor geographical and general knowledge western societies had about Africa and about promoting air travel.

Dornier-Werke Friedrichshafen and the Bayerische Motoren Werke in Munich were the main sponsors, but Mittelholzer could not count on the support by the colonial authorities. The Dornier Merkur "Switzerland" reconfigurated as a seaplane granted him independence from airfields. He carefully planned his journey along the Nile, lakes and the open sea.

Mittelholzer, who was a photographer before he became pilot, had the latest photographic and filming equipment on board, including large-format cameras and special equipment for mapping shots, as well as a fully equipped darkroom.

The trip proved to be challenging. Equipped with a inaccurate maps with a scale of 1:1 000 000 and without any infrastructure along the route, most of the 23 laps were very much into unchartered areas. Especially when it comes to flying. But the Dornier Merkur with its BMW engine proved to be very reliable and the expedition arrived safely in Cape Town on the 21 February 1927. Mittelholzer leaves us with a unique collection of photographs and films of the time.

The original propeller of the Dornier Merkur is exhibited in the international departure hall of the Cape Town airport.
Variants
Do C III Komet I
First of the Komet series



Do Komet II




Do Komet III
larger, more powerful four-six passenger version.






Do B Merkur I




Do B Bal Merkur II





























Do C
Military version of the Komet III

Do C-1: Two-seat fighter.
Do C-2A: Recognition version.
Do C-3: Recognition version.
Do C-4: Do-10, development of C-1.
Do D
A much revised floatplane torpedo bomber version for the Royal Yugoslav Air Force.



Do T
An ambulance version




Komet II
Engine: 1 x BMW IV, 185kW
Take-off weight: 2200 kg / 4850 lb
Empty weight: 700 kg / 1543 lb
Wingspan: 17.0 m / 55 ft 9 in
Length: 10.3 m / 33 ft 10 in
Height: 3.3 m / 10 ft 10 in
Wing area: 50.0 sq.m / 538.20 sq ft
Max. Speed: 165 km/h / 103 mph
Cruise speed: 135 km/h / 84 mph
Ceiling: 5000 m / 16400 ft
Range w/max.fuel: 500 km / 311 miles
Crew: 1
Passengers: 4
Do.B Merkur
Engine: 1 x BMW VI, 500kW
Take-off weight: 3700 kg / 8157 lb
Empty weight: 2280 kg / 5027 lb
Wingspan: 19.6 m / 64 ft 4 in
Length: 12.8 m / 41 ft 12 in
Height: 3.8 m / 12 ft 6 in
Wing area: 62.0 sq.m / 667.36 sq ft
Ceiling: 5200 m / 17050 ft
Range w/max.fuel: 1000 km / 621 miles
Crew: 2
Passengers: 6-7