April 28th.
Under repeated urging from MacArthur, the security forces, with cover from the US Seventh Fleet and Army Air Forces, launched Operation Oboe, advancing on Borneo from the east. Without this American backing, the Chinese contingent would never have been given the opportunity to land.
The landing site on May 1st was at Tarakan, in northeastern Borneo. The May 1st landing, conducted under Allied naval gunfire support, went extremely smoothly. The Japanese Navy garrison defending the Lingkas Beach on Tarakan Island offered only brief resistance before retreating.
The 3rd Reinforced Brigade suffered negligible casualties during the entire landing operation. The first day's skirmishes were less a true landing and counter-landing than a probing action, which matched the initial assessment: to avoid the Allies' overwhelming artillery advantage, the Japanese would deploy their main forces inland.
