He then commanded the hydrographic survey ship Vegas, before being sent to Britain in 1958–59 to attend the British Royal Navy's Navigation School.

In the latter capacity he received a commendation from the Chief of the Hellenic Navy General Staff and the Minister for Mercantile Marine for his role, despite extremely difficult weather conditions, in the rescue of the crew of the steamer Stratoniki, which sank on 7 September 1967.

In 1971 he graduated from the NATO Defense College, and in 1971–72 he headed the Navy's Training Centre at Poros and the Naval NCO Academy.

[1] In 1972 Pappas assumed command of the destroyer Velos, with which he participated in the abortive Navy revolt, planned for 25 May 1973, against the then-ruling military junta.

Although the revolt was pre-empted by the junta, Pappas led his own vessel, the destroyer Velos, to Italy, where he and 31 of the ship's officers and NCOs requested political asylum, and gave a press conference in front of the international media where he denounced the regime.