A native of County Roscommon, he was an explosives expert and reputedly invented the "Irish War Flour" and "Irish Cheddar" devices. He subsequently became IRA Director of Chemicals in 1921. During the Irish War of Independence he was imprisoned in Mountjoy and Kilmainham prisons and later interned in Newbridge, County Kildare. He opposed the Anglo-Irish Treaty and fought in the Irish Civil War. In 1930 he became manager at ESB headquarters in Dublin. In August 1938, at the request of IRA chief of staffSeán Russell, he wrote the S-Plan, a bombing campaign targeting England. During this time O'Donovan and Russell were the only GHQ members of the old IRA still in the organisation. In his unpublished memoirs he wrote that he "conducted the entire training of cadre units, was responsible for all but locally-derived intelligence, carried out small pieces of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.
Involvement with Abwehr
As "Agent V-Held", he visited Germany three times in 1939 on behalf of the IRA. On 28 February he negotiated an arms and radio equipment delivery at the Abwehrstelle in Hamburg. On 26 April he concluded a new arms deal with the Abwehrstelle and established, with the help of a Breton, a secret courier connection to Ireland via France. On 23 August, O'Donovan received the last instructions for the event of war. On 9 February 1940, Abwehr II agent Ernst Weber-Drohl landed at Killala Bay, County Sligo aboard U-37. He was equipped with a 'Ufa' transmitter, cash, and instructions for O'Donovan. 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. O'Donovan became increasingly enamoured of Nazi ideology during this time, and visited Germany three times. In 1942 he 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". Even long after the pact with the Germans fell apart, O'Donovan continued to express his sympathy for the Nazi regime. His son, Gerard O'Donovan, recalled that every Saturday night a visitor would come to the family home and send messages to Germany. In 1940, he was involved in setting up Córas na Poblachta, a party which proved unsuccessful.
