The Christmas Raid was an attack on 23 December 1939 by the Irish Republican Army (IRA) against the Irish Army and the Phoenix Park Magazine Fort—Ireland's largest munitions dump. The attack resulted in the capture of the munitions dump by the IRA and the seizure of a huge quantity of weapons. Although the operation was initially successful, two of the raiders were captured shortly after the raid and, in the following days, most of the stolen military equipment was recovered and several IRA volunteers were arrested.

The Dublin Magazine Fort was built in 1735. The fort is in the west of the city, north of the River Liffey within Phoenix Park. The building is located in the south-eastern part of the park, close by a wooded ridge, and has a commanding view of the surrounding area. It was occupied by the British Army during the period of British rule, and after independence was utilised by the Irish Army to store their stocks of arms and ammunition.

The IRA was still involved with the Sabotage Campaign at the time of the raid, with a lot of units either interned, on the run, in Britain, or recently deported from Britain. A number of members of the Army Council were also on the run, trying to evade capture by the Garda Síochána (Irish police). The stated reason for a raid on the Fort being ordered was that, although the IRA had many Thompson submachine guns (imported with the help of Clan na Gael over the preceding decade), the .45 ACP ammunition used in these guns was not easily available in continental Europe. It so happened that the Irish Army also used the Thompson and had large supplies of ammunition. Permission was sought to steal ammunition, either from the Magazine Fort or nearby Islandbridge Barracks. Acting Chief of Staff in Seán Russell's absence, Stephen Hayes, gave the order.

A raid on the Fort was not a new idea—it had been floated initially in 1937, but IRA Chief of Staff Mick Fitzpatrick had dismissed the idea as unworkable, because there would be nowhere to store the stolen ammunition. Hayes, on hearing that the raid was possible, felt he should take the risk. The Christmas season was chosen as the perfect time for the operation, as security was expected to be even more lax than usual. However, the people operating the arms dumps had not expected the sheer amount of weaponry taken during the raid.

Many IRA members had been interned under the Offences against the State Act 1939 on the outbreak of the war, but released in December when the Supreme Court ruled in State (Burke) v. Lennon that the relevant section of the 1939 act violated the constitution. Some of those released participated in the raid.

The Magazine Fort did not have its own guard troops. These were supplied from infantry units stationed in the Command area. That particular night, the 7th (Dublin) Infantry Battalion, a reserve battalion stationed at Portobello Barracks (now Cathal Brugha Barracks), was responsible for supplying the guard, and the fire picket was supplied by a unit stationed in Islandbridge Barracks (now Clancy Barracks).

On the evening of the Raid, the officer responsible for the defence of the fort, the same man who had filled the post for twenty-four years, had the following at his disposal for guard duty:

The guard party were warned for duty on the evening of 22 December and given precise instructions as to their duties for the next morning.