Degiannis had participated in the abortive pro-Republican coup attempt of March 1935, and been dismissed from the navy as a result.
Due to the German invasion of Greece and the rapid conquest of the country in April–May 1941, the British were not able to organize their clandestine network on a firm basis or provide them with suitable material such as radios.
Degiannis, along with fellow participants in the 1935 coup Charalambos Koutsogiannopoulos and Dimitris Bardopoulos, was left in charge of the group which was reorganized as "Prometheus II".
The group collected intelligence for the SOE and engaged in a successful sabotage campaign against Axis shipping.
In December 1980 the Hellenic Navy commissioned the La Combattante IIIb-class fast attack craft Ypoploiarchos Degiannis (P 26) in his honour.