During the Axis Occupation of Greece, he participated in the Omiros resistance group, and in 1944 he fled to the Middle East and joined the elite Sacred Band of the Greek government in exile.

Promoted to lieutenant colonel in the same year, he was placed for a while as aide de camp to Marshal Alexandros Papagos, followed by command of the 391 Tank Regiment.

[1] From this position, Spandidakis became the driving force behind the Army's plans to seize power in view of the ongoing political crisis in the country, under the codename IERAX II.

The Army hierarchy, supported by King Constantine II, feared the growing influence of the left, particularly after the Apostasy of July 1965 and the rising anti-palace sentiment among the populace.

Spandidakis promoted several officers who would later play a leading role in the coup d'état of 21 April 1967 to key positions; most notably the then-Lieutenant Colonel Georgios Papadopoulos.

[2] Nevertheless, Spandidakis was caught by surprise by the outbreak of the military putsch of 21 April 1967, which the group of mid-level officers around Papadopoulos initiated without waiting for authorization by the King and the Army leadership.