Oplan Merdeka was the failed attempt by the disgraced President Ferdinand Marcos of the Philippines to conduct a terrorist campaign on the state of Sabah in the 1960s. It was a project that would have pitched the Philippines not just against Malaysia, but also Britain, Australia, New Zealand, and Singapore. It was a foolhardy effort and Malaysia and its allies had seen off an attempted Communist takeover in the Malayan Emergency and an invasion by Indonesia during the Konfrontazi.
The scheme was shattered by the massacre of Muslims on Corregidor who were recruited to terrorise Sabah, known as the Jabidah Massacre. While revisionists like the notorious Roberto D. Tiglao of the pro-Marcos Manila Times claim the whole thing to be a hoax, the evidence for it is solid.
There were brief flash reports on radio broadcasts but the story was suppressed early enough to keep it out of print media. The incident became common knowledge. The suppressed story broke through when Senator Ninoy Aquino, former journalist, gave a privilege speech in the Senate.
After the embarrassing incident on Corregidor, there was a secret court martial of those involved, blood-money was paid to the families of those who were executed, and the prosecutor in that case is still alive.
The video below has technical issues, for which I apologise, but it demolishes the claim that the massacre never happened.