In 1917, aged 16, Donegan left Bantry to study national school teaching in De La Salle College Waterford.
During the Conscription Crisis of 1918 Donegan returned to Bantry, undertaking Irish Volunteers training with Raphael Keyes.
At this time Donegan was also involved with an Irish Volunteers training camp, held in Glandore in August 1919.
[2][3] On 28 March 1920, Ted Sullivan and Donegan organised an attack on a Royal Irish Constabulary barrack in the village of Durrus.
[2] When the IRA arrived in Glengarriff they occupied two points on the main street where they were engaged in gunfire with the RIC patrol.
[6] While detained at Belfast Docks, members of the Orange Order gathered to beat the prisoners using iron bars.
At one stage recording devices were discovered in the walls of common areas and so the council tied notes onto stones, relying on good aim to pass messages.
[2] Donegan and Colgan were arrested in Drogheda by the RIC, and were returned to Ballykinlar where they served six weeks solitary confinement while awaiting trial.