S Plan

In 1938 MacGrath was the IRA’s Adjutant general and oversaw the bombing/sabotage campaign in England from the IRA GHQ.^[8] MacGrath worked on planning the "English Campaign" or "S-Plan" which targeted the civil, economic, and military infrastructure of the United Kingdom (specifically England). MacGrath was reputed to be one of the principal instructors in bomb making for this campaign.^[9][10] Two week classes were conducted in Dublin by Seamus O'Donovan and Paddy MacGrath.^[11] This bombing campaign took place from January 1939 to March 1940 involved approximately 300 explosions resulting in 10 deaths, 96 wounded and substantial damage to English infrastructure.^[12] As a result of the bombings in England, in 1939 the Irish government increased pressure on the IRA leading to MacGrath's arrest and quick execution.

Second arrest and hunger strike

MacGrath was arrested on 22 October 1939 and went on hunger strike that same day, vowing that he would have his freedom or die.^[13] Interned in Arbour Hill Prison under the Offences against the State Acts 1939–1998, MacGrath went on hunger strike.^[14] On 15 November 1939 was removed to Jervis Street Hospital and on 4 December 1939 (after 43 days without food) escaped from the hospital with the assistance of a Republican sympathiser on the staff of the hospital.^[15] Three days later the government filed a request for non prosecution (Nolle prosequi) at Special Criminal Court.^[16]

Third arrest, trial and execution

Paddy MacGrath was an important leader during the IRAs S-Plan attacks on England. MacGrath provided IRA men with training and worked on logistical support. On 17 August 1940 MacGrath was again arrested at a house 98A Rathgar Road, Dublin by Special Branch detectives^[17] during another raid on the IRA's General Headquarters (GHQ).^[18] IRA Volunteer Thomas Harte was also arrested at that time and was later executed with MacGrath. They had been arrested after a gun battle with Garda Síochána (police) Special Branch in which Detective Sergeant Patrick McKeown and Detective Garda Richard Hyland were shot dead. Detective Garda Michael Brady was also wounded. As the two IRA men attempted to escape, MacGrath returned to assist the wounded Harte and both were arrested.^[19] Another IRA man (Tom Hunt) escaped but was subsequently arrested and also charged with the murders but had his death sentence commuted on the morning of execution and was interned in the Curragh prison camp. The topic of the meeting at the GHQ was reportedly planning to support "Plan Kathleen" which was a notional plan by the Nazis to invade Northern Ireland.^[20] At the time of these arrests Stephen Hayes (Irish republican) was the IRA Chief of Staff. On 30 June 1941, Northern-based IRA men kidnapped Hayes, accusing him of being a spy for the Irish Government.^[21] In his written confession Hayes admits to providing the address of the meeting to government officials which resulted in the capture Harte, McGrath and Hunt.^[22]

Harte, MacGrath and Hunt were tried by Military Tribunal, established under the Emergency Powers Act 1939. All three men were represented in court by Seán MacBride. They challenged the legislation in the Irish High Court, seeking a writ of habeas corpus, and ultimately appealed to the Irish Supreme Court. The appeal was unsuccessful (at that time there was no right to appeal the findings of a Military Tribunal), Harte and MacGrath were executed by firing squad at Dublin's Mountjoy Prison on 6 September 1940 (22 days after the shooting).^[23] MacGrath was buried in an unmarked grave in the prison yard. In 1948 his remains were released to his family, he is buried in Glasnevin Cemetery next to the graves of Seán MacBride and Maud Gonne.^[24]