[7] In August 1938, at the request of IRA chief of staff Seán Russell, he wrote the S-Plan, a sabotage/bombing campaign targeting England.

[9] In his unpublished memoirs he wrote that he "conducted the entire training of cadre units, was responsible for all but locally-derived intelligence, carried out small pieces of research and, in general, controlled the whole explosives and munitions end" of S-Plan.

The transmitter was lost upon landing, but when Weber-Drohl reached O'Donovan at Shankill, Killiney, County Dublin, he was able to deliver new transmission codes, $14,450 in cash, and a message from "Pfalzgraf Section" asking that the IRA concentrate its S-Plan attacks on military rather than civilian targets.

[13] In 1942, O'Donovan wrote an article arguing that Ireland's future lay in an alliance with a victorious Germany and attacked Britain and the United States for being "centres of Freemasonry, international financial control and Jewry".

His son, Gerard O'Donovan, recalled that every Saturday night a visitor would come to the family home and send messages to Germany.

[15] In 1940, he was involved in setting up Córas na Poblachta, a short-lived fringe political party formed in 1941 by IRA members opposed to what they saw as "de Valera's collaboration with Britain".