[1] Notable incidents during his tenure include the Pata Island massacre,[10][11] the assassination of Zamboanga City Mayor Cesar Climaco,[12][13] the rescue of kidnapped Bishop Federico O. Escaler[14] from Muslim rebels and the strafing of the Japanese vessel Hegg by Philippine Air Force fighters off Mindanao.

His sister, Gloria, later married Teodulfo Bautista, a fellow graduate of the Philippine Military Academy (PMA) from Marikina who would become a close friend to Castro.

The graduation date was advanced a month earlier to meet the requirement for platoon leaders very much needed because of the growing insurgency threat posed by the Communist Party of the Philippines and its military arm, the Hukbong Magpapalayang Bayan (HMB).

A break in this campaign resulted only when he was fielded to the Korean War in March 1953 where he initially served as a platoon leader of Quad 50, 145th AAA (Artillery & Antiaircraft) Battalion,[21] 45th Infantry Division, US Army.

[22] He was eventually assigned as a platoon leader of the Recon Company, 14th Battalion Combat Team (BCT), Philippine Expeditionary Forces to Korea (PEFTOK)[23][24] under Col. Nicanor Jimenez.

In Vietnam, Castro was the Liaison Officer for Operations and Intelligence with Free World Military Assistance Headquarters, MACV from 1966 to 1968.

His assignment included coordination with US Government Embassy Liaisons Edward Lansdale and Napoleon Valeriano,[citation needed] his former battalion commander.

In 1969, he served with J2 AFP under Gen. Rafael Ileto and Gen. Fidel V. Ramos as Head of the Production Branch (Research), which gave him also the opportunity to sit with the 14th Intelligence Assessment Committee of SEATO in Bangkok, Thailand.

Upon his return to the Philippines, he was immediately fielded south in Mindanao where an insurgency by the Moro National Liberation Front (MNLF) headed by Nur Misuari had escalated.

During these years of service in Mindanao, General Castro had survived several hostile fires airborne and on the ground, plane mishaps and a helicopter (Huey UH1H) crash.