It was developed for the Luftwaffe, but Deutsche Luft Hansa received five aircraft and used these for tests between the Azores and the North American continent in 1936 and on their mail route over the South Atlantic from 1937 to 1939.

On 27–29 March 1938, a "Do 18 W" established a seaplane record, flying non-stop a straight distance of 8,391 km (5,214 mi) from Start Point, Devon to Caravelas in Brazil.

[4] The Do 18c was delivered to Deutsche Luft Hansa as a Do 18E civil transport (D-ABYM Aeolus), quickly followed by a further two aircraft, (D-AANE Zyklon and D-ARUN Zephir)[5] with a final Do 18E (D-AROZ Pampero) being built in 1938.

[6] It was later modified with 656 kW (880 hp) BMW 132N radial engines to test a possible upgrade for the Luftwaffe's aircraft, flying in this form on 21 November 1939 as the Do 18L.

[7] In 1936, Deutsche Luft Hansa started a series of endurance trials, culminating on 10–11 September when Zephir, flown by Flugkapitän Blankenburg with Deutsche Luft Hansa Director Freiherr von Gablenz as passenger, was launched by catapult from the seaplane tender Schwabenland at Horta, Azores, flying the 4,460 km (2,270 mi) to New York City in 22 hours 12 minutes.

In April 1937, D-ARUN Zephir and D-ABYM Aeolus started service on the South Atlantic mail route from Bathurst, now Banjul, Gambia to Natal, Brazil (3040 km).

Catapult ships were based in Bathurst and Fernando de Noronha to allow the aircraft to cross the Atlantic carrying a full load of mail.

Aeolus was lost on 30 July 1937, when it had to make an ocean landing due to engine problems and was heavily damaged when Ostmark tried to retrieve the plane.

On the way back to the South American station the seaplane tender Westfalen took the aircraft into the English Channel where it was catapulted to Brazil.