Van Diemen is best remembered for his efforts to foster exploration of the "Great South Land", Australia, resulting in "the final and most ambitious Dutch voyages of the century".[3] The first voyage under his energetic administration was undertaken within three months of his arrival in Batavia; starting from Cape York its ships were to chart the unknown coasts, but the venture ended in failure, when its commander was killed by natives in New Guinea, and the ships returned. In 1639 he commissioned two voyages to the north, in search of the "Gold and Silver Islands" that Spanish reports placed in the North Pacific to the east of Japan, and sent Maarten Gerritsz Vries to explore the coasts of Korea and "Tartaria"; these, too, returned fruitlessly.[3] Undeterred, Van Diemen appointed Frans Visscher to draw up a plan for new discoveries.