1 Belfast Brigade – 3 Northern Division
1 Brigade, 3 Northern Division was located in Belfast and consisted of four battalions and an Engineering Battalion. The strength of the Brigade on 11 July 1921 was 924 all ranks and the strength of the Brigade on 1 July 1922 was 436 all ranks. No data is available for 3 and 4 Battalions which were said to have been organised between 11 July 1921 and 1 July 1922 and not to have existed on either critical date.
1 Battalion: Unit strength on 11 July 1921 was 579 all ranks, and the strength on 1 July 1922 was 282 all ranks. The companies of the 1 Battalion were all located within the City of Belfast.
2 Battalion: Unit strength on 11 July 1921 was 303 all ranks and the strength on 1 July 1922 was 38 all ranks. (Note: only one company of the original four is shown as remaining on the second critical date). The companies of the 2 Battalion were all located within the City of Belfast.
3 Battalion: No data.
4 Battalion: No data.
Engineering Battalion: Unit strength on 11 July 1921 was 36 all ranks and the strength on 1 July 1922 was 110 all ranks. There is one company of the Engineering Battalion listed and it was located within the City of Belfast.
1 Belfast Brigade – 3 Northern Division Featured Operations
1 Belfast Brigade – 3 Northern Division Operations List (includes those not featured on the map)
| Operation | County | Location | Date | |
| Attack on RIC at Roddy’s Hotel, Belfast | Antrim | Oxford Street, Belfast | 26 January 1921 | |
| Shooting of M.P. in Belfast | Antrim | Lower Garfield Street, Belfast | May 1922 | |
| Attack on Special Constabulary at May Street, Belfast | Antrim | May Street, Belfast | 23 March 1922 | |
| Attack on Special Constabulary at Victoria Square, Belfast | Antrim | Victoria Square, Belfast | 11 March 1921 | |
| Police Sergeant shot Mulholland Terrace, Belfast | Antrim | Mulholland Terrace, Belfast | March 1922 |