G Division

G (detective) Division was a plainclothes divisional office of the Dublin Metropolitan Police concerned with detective police work. Divisions A to F of the DMP were uniformed sections responsible for particular districts of the city.

By 1859 much of the G Division's work was concerned with Fenianism. Superintendent Daniel Ryan headed the detectives answering to Sir Henry Lake, chief commissioner of the Dublin Metropolitan Police (DMP). Ryan had an informer named Pierce Nagle within the offices of the Fenian Irish People newspaper. In 1865 Nagle warned Ryan about an “action this year” message on its way to the Irish Republican Brotherhood unit in Tipperary. On 15 July 1865 Irish American plans for an IRB rising in Ireland were discovered when the emissary lost them at Kingstown railway station. Ryan raided the offices of the newspaper on 15 September and the staff were arrested. They were tried and sentenced to terms of penal servitude.

In 1874 John Mallon succeeded Ryan as head of G Division. Mallon's father had been linked with the Ribbon Society but the son had specialised in his career working against Irish republicanism. He had an extensive knowledge of the separatists and operated a personal network of spies and informers. In the 1880s G Division was pitted against separatist insurgents including the Invincibles. It also operated against the Land League and even the Irish Parliamentary Party, arresting Charles Stewart Parnell in 1881. Mallon supervised G Division until his retirement in January 1902. To protect his informants, Mallon had refused to commit much of his knowledge to paper.

The unarmed and uniformed majority of the Dublin Metropolitan Police played a relatively neutral role during the troubles of 1919, restricting their functions to such traditional roles as criminal investigation and traffic control. However an expanded G Division was employed as an active intelligence agency against the IRA. In his book "The Spy in the Castle" David Neligan (an IRA double agent who infiltrated G Division) suggests that much of this activity was unprofessional, dependent upon casually recruited local spies and English officers whose wartime experience in Cairo and elsewhere had little relevance to Dublin conditions.

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