[3] From 11 August to 12 November 1920, Crowley, along with 10 others, underwent a hunger strike for 94 days in Cork County Gaol, demanding the reinstatement of their political status and release from prison.

Through this period, Crowley made ammunition and cut communications lines in preparation for attack on Royal Irish Constabulary (R.I.C.)

As a consequence of this, he was arrested by British forces at Ballylanders in July 1916 and detained in the Military Detention Barracks Cork for two weeks.

Over the course of 1 April 1917 to 31 March 1918, Crowley, now under Donnchadh Hannigan, took part in raids for arms, ammunition and equipment, which he then took care of and protected.

He was engaged with the attack on Kilmallock Barracks as well and took part in defending his father Timothy Crowley's house in Ballylanders when it was bombed by British forces on 6 July 1920.

He was tried by court martial on the charge of taking part in an attack with firearms on Crown forces and was sentenced to three years in prison, where he underwent what would become the longest hunger strike in history, lasting 94 days.

He was involved in no military engagements, and spent around ten days recovering in the Mater Hospital in Dublin from his hunger strike.

From 1 April to 30 September 1923, Crowley was unable to render any active service due to his ill health and was medically advised to leave the country.

On his 1935 pension application, he wrote that he was receiving a weekly salary of £2, 8 shillings and 7 pence as a paper keeper in the Department of Industry and Commerce.

[6] By the outbreak of the Civil War, Crowley, having been medically advised to leave Ireland, was living in the Bronx, New York, and working as a ticket agent for the Interborough Rapid Transit Company.

[7][failed verification][better source needed] He married Minnie Daly (1906-1991) in 1928, and their first son, Peter Maurice Crowley, was born in New York in December 1929.

Crowley, believing that the "foot soldiers" of the war would be rewarded under the new Fianna Fáil government, returned to Ireland against the wishes of his wife Minnie, who wanted to stay in New York.