On February 8, 1967, President Marcos rescinded Executive Order No.207 of 1939, and promulgated Executive Order No.59. The EO made ROTC a mandatory course at all colleges and universities and other institutions with an enrollment of 250 male students.

A noteworthy development during the Marcos years was a program called the Rainbow Rangers – Sunday Soldiers. The Metro Manila-only unit provided an alternative to ceremony-centric conventional ROTC training, and was one of the earliest attempts to address inadequacies in the ROTC program. The UP ROTC formed the RR – SS on September 15, 1968, under the watchful eye of then Captain (later Brigadier General) Benjamin Vallejo. The unit included students from other schools, such as long time rival UST ROTC.

Trainees, who were all volunteers, were subjected to a more aggressive, combat-oriented, training regimen that exposed them to small-unit tactics, unconventional warfare, and home defense techniques. To add to the realism, the RRs were given access to real weapons.

Though based in Manila, it saw action in places as far as Mindanao. The unit formed the backbone of the “Liberator Battalion”, that took part in a 3-week peacekeeping operation in the Lanao provinces during the November elections in 1971. Members of the battalion reportedly earned 9 citations for bravery during the operation.

For the most part, training was conducted at the University of the Philippines. Towards the end of the unit's life, the venue was moved to the Metropolitan Citizen Military Training Command (MCMTC) compound. The unit was disbanded circa 1983, after General Vallejo’s retirement.