Sidney Sarah Madge Czira (née Gifford; 3 August 1889 – 15 September 1974), known by her pen name John Brennan, was a journalist, broadcaster, writer and revolutionary.

Her articles varied from those highlighting poor treatment of women in the workplace to fashion and gardening columns, some written under the pseudonym Sorcha Ní hAnlúan.

Its members learned first aid, drilling and signalling and rifle shooting, and served as an unofficial messenger and backup service for the Irish Volunteers.

During the fight for Irish Independence the women carried messages, stored and delivered guns and ran safe houses where men on the run could eat, sleep and pick up supplies.

Through her connection with Padraic Colum and Mary Colum, whom she had met through her brother-in-law Thomas MacDonagh, she met influential Irish-Americans such as Thomas Addis Emmet and Irish exiles like John Devoy, and married a Hungarian lawyer, Arpad Czira, a former prisoner of war who was said to have escaped and fled to America.

She and her sister Nellie Gifford founded the American branch of Cumann na mBan, and she acted as its secretary.

In the 1950s her memoirs were published in The Irish Times, and she moved into work as a broadcaster and produced a series of historical programmes.