Operation Oaktree

Under the command of Captain Jean Victor de Bruijn, some 40 soldiers operated in the highland region of Western New Guinea for more than two years between December 1942 and July 1944, handled by the Netherlands East Indies Forces Intelligence Service, with Australian assistance.

[7] At that time, all the planes in Australia were required either by General Douglas MacArthur or the Australian government to fight in Eastern New Guinea and the Solomon Islands.

[8] When de Bruijn came back to the highlands, he found out that because of his departure, the natives had been convinced by the Japanese to report directly to their headquarters in Fakfak,[9] which they had occupied in April 1942.

De Bruijn did not know until he reached the post that the Japanese, angered by his raid on Oeta, had sent Zero fighters and floatplanes on reconnaissance flights over the lake in order to show their awareness of his presence there.

However, in early 1943, Japanese reconnaissance aircraft were making long passes over the lakes, often flying below 150 feet, taking photographs for a planned occupation.

De Bruijn subsequently radioed the Netherlands East Indies Forces Intelligence Service HQ in Australia, which started realizing the importance of his mission in the highlands.

[18] The Oaktree party was now getting stronger, fortified by new radio sets, food, rifles, and military training, reaching about 40 men strong, who were based at Bilorai.

One day, east of Bilorai, the Japanese were ambushed during their sleep by a patrol of two Indonesians and five Papuans, killing fifteen with Thompson submachine guns and hand grenades.

[21] At the same time, native observers reported that more and more Japanese troops were moving toward the mountains, fleeing from their strongholds on the northern coast at Hollandia and Sarmi, which had been invaded by the Americans.

However, Western New Guinea was spared by the fighting, as the Dutch still enjoyed popularity among the native population, and remained in their hands until 1962, before its transfer to Indonesia the following year.