Although the order by the ML-KNIL was cancelled, the Luchtvaartafdeling (Dutch Army Air Force before World War II) placed an order of 36 aircraft, which were all delivered in time to participate in the war against the Germans in May 1940.
In October 1943, Van Oyen was promoted to Lieutenant general and deputy army commander of the KNIL, replacing Lieutenant General Hein ter Poorten, who at that time was taken prisoner by the Japanese.
He was the son of KNIL general Marinus Bernardus Rost van Tonningen, who had distinguished himself suppressing the revolts against Dutch rule on Lombok, Aceh and Bali.
The Dutch counter-insurgency offensive was masterminded by the controversial Raymond Westerling, a Captain in the KNIL (Royal Netherlands East Indies Army).