These patrols—which were highly classified at the time—often involved small reconnaissance teams crossing the border from the Malaysian states of Sarawak or Sabah into Indonesian Kalimantan in order to detect Indonesian forces about to enter East Malaysia. Initially, penetration was limited to but was later extended to , and again to after the Battle of Plaman Mapu in April 1965. Conventional follow-up forces of platoon and company size were then directed into position to ambush the Indonesians, either as they crossed the border or often while they were still in Kalimantan. Such operations were to be "deniable" and were conducted under a policy of "aggressive defence". Given the sensitivity of these operations and the potential consequences if they were exposed, they were controlled at the highest level and conducted within strict parameters known as the "Golden Rules", while the participants were sworn to secrecy.