The Double Sunrise

The Double Sunrise service was formed in 1943 to re-establish the Australia–England air link that had been cut due to the fall of Singapore in 1942. The service initially operated from its base in Nedlands, Western Australia near Perth, to the Royal Air Force base at Lake Koggala near Galle in Ceylon (now Sri Lanka). It was later extended to Karachi in India (now part of Pakistan), which was the terminus for the BOAC service from England. The name of the service was derived from the crew observing two sunrises on each flight.

In 1943, Royal Australian Air Force personnel were seconded to operate Consolidated PBY Catalina amphibian seaplane aircraft under the banner of Qantas. The plan called for flights between Crawley, Western Australia, and RAF Base Koggala in southern Ceylon. The flights were (then) the longest non-stop air route of any airline, over 3,500 nautical miles (6,480 km, 4,020 mi) across the Indian Ocean. Navigating without the aid of radio, the crews relied solely on rudimentary navigation by compass and stars during the trip.

Taking between 27 and 33 hours, with departure timed so that the flight crossed Japanese occupied territory during darkness, the crews would observe the sunrise twice, which led to the service being known as "The Double Sunrise". The flight route flown was along the coast from Crawley to Exmouth then setting out towards Cocos (Keeling) Island or Christmas Island (though neither was actually sighted during the flight) and onto Galle, a journey of approximately 3,580 nautical miles (6,630 km; 4,120 mi). After the success of the initial flights, it was decided to run a weekly service, with some services flying over Rottnest Island and then taking a direct line to Galle. As part of the Australia-England air route there was a surface component from Galle to Karachi that added considerable time to the service. This was later replaced by the Double Sunrise service, with Karachi to England flown by BOAC. Air crews would change in Galle taking the next plane in either direction minimizing the time taken to complete the journey.

...
Wikipedia