He entered the Reserve Officer Service School (ROSS) at Camp Henry T. Allen in Baguio City, where he was made the battalion commander.

Two days after, he was decorated with the United States Army's Distinguished Service Cross for "extraordinary heroism in combat in Bataan" and the Silver Star for "gallantry in action".

During the Japanese occupation from December 1942 to January 1945, he joined the Filipino-American Irregular Troops (FAIT) under Col. Hugh I. Straughn as chief of the Intelligence Division of the North Section in Manila, with the rank of colonel.

When Congressman Datu Mangelen and Senator Salipada Pendatun offered him the provincial governorship of Cotabato in 1951, through then Secretary of National Defense Ramon Magsaysay, he declined.

Santos knew what he wanted in his career and to him a diversion like that of the appointive offer would adversely affect his plan to attain the highest position in the military hierarchy.

He made history when Guillermo Capadocia, erstwhile secretary general and one of the founders of the Communist Party of the Philippines (CPP), was captured at Barrio Yubog in San Remigio, Antique.

During the hectic campaign to capture Capadocia and destroy the leftist band in 1951 and 1952 on Panay Island, Colonel Santos made one crucial decision which ensured the success of the operations.

The incessant military operations aimed primarily at the capture, whether dead or alive, of dissident leaders resulted in the surrender of hundreds of their men.

In addition, the capture of the rebels' arms, supplies and equipment as well as important documents which were of great value to the entire campaign for peace and order throughout the country was crucial in breaking up the backbone of the dissidents' depredations in Visayas and Mindanao.

Under cover of the typhoon, a scout ranger team (Rafael Ileto's) positioned itself at the latrine area of his camp and caught him in their sights literally with his pants down.

Colonel Santos' deep understanding and full knowledge of the nature of the dissident underground movement enabled him to effect the intelligent deployment of his troops as well as secure the cooperation and support of the civilian population and weakening the Huk organization.

Through his conscientious and indefatigable efforts, he efficiently carried out the broad policies and vital mission of the PA, particularly the build-up and training of the Citizen Army and the implementation of the socio-economic military program of the AFP.

To better prepare military personnel for civilian life, he pursued non-military projects that could provide opportunities to soldiers and reservists especially upon their retirement or separation from the service, in the form of practical lessons and training in livestock-raising.

His firm, mature and unyielding decisions on administrative matters, which were tempered with and founded upon justice and human understanding, contributed to a large extent to the effective synchronization of the various PA staffs and efficient functioning of the entire command.

He received the Certificate of Honor from US Ambassador Henry A. Byroade in simple ceremonies held at the US Embassy, Roxas Boulevard, Manila, on April 14, 1973.