Mt Wilhelmina to the Idenburg River (a tributary of the Mamberamo River), making collections at altitudes from near sea-level to over 4,000 m at the upper limit of vegetation. Piloted by Russell R. Rogers, the expedition used a PBY-1 Catalina flying boat (named Guba II), that could land on suitable lakes and rivers, to provide supplies to the expedition, as well as performing other duties such as aerial reconnaissance and photography. It was through an aerial reconnaissance flight early in the expedition that the discovery was made, on 23 June 1938, of the hitherto unknown, though densely populated, Baliem Valley, home to the Dani people. A Dutch soldier on board the Guba named the valley Groote Vallei, or Grand Valley, and Archbold declared that would be its name. In August 1938, Archbold dispatched two exploration teams, each consisting of Dutch soldiers, convicts, and Dayak porters, into the Baliem Valley. One team led by Captain C.G.J. Teerink started at one end of the valley, while the other, led by Lieutenant J.E.M. Van Arcken, started at the other end with the goal of meeting in the middle of the valley. On August 10, 1938, an incident occurred near the valley's center resulting in the death of a Dani tribesman. Pioneer flight over the Indian Ocean Towards the conclusion of the expedition in 1939, with Archbold intending to return to the USA across the Pacific, he was contacted by Captain P.G. Taylor, representing Australian interests which, with war impending, wanted to determine the practicality of an air route from Australia to Europe over the Indian Ocean and via Africa rather than Asia. It appeared that Guba II was the only suitable aircraft for the job at short notice. As Archbold was amenable to the project, his aircraft was effectively chartered for the crossing by the Australian government (which paid for fuel and other provisions used during the flight) and his flying crew augmented by Taylor as navigator. The intended flight path across the Indian Ocean was from Port Hedland, Western Australia to the Cocos (Keeling) Islands, Diego Garcia, the Seychelles and Mombasa, Kenya. Apart from the initial leg of the flight, when the plane was forced, after leaving Port Hedland, to detour via Batavia (now Jakarta) because of bad weather, the flight was made without major problems. In Mombasa, Taylor left the crew to return to Australia and Archbold continued the flight westwards,