The Irish military has participated in most United Nations military or peace-keeping operations since 1949. Not only does this fulfill the obligation to support the United Nations, but it also keeps equipment up-to-date and personnel trained in real-world situations. The latter is very important, since as a small country that is not in NATO, Ireland is often left out of the exercises and situations that cannot be covered in textbook or peacetime classroom training. While the rest of the European military is coordinated through Standard NATO Agreements (STANAGs), and inter-operable, this provides an channel for Irish participation. In short, providing troops for UN support is a "win-win" situation.
Another benefit is that it places Ireland as a participant on the world stage. Irish personnel are exposed to challenging situations, and encounter people in different environments. This forces politicians to insure that their armed forces are maintained at a certain level of readiness and training. It also benefits trade since the logistical support of troops causes Irish industries to think globally, and develop trade routes, capabilities, and equipment that may develop into sales.
For the postal historian, Irish letters and packages provide an interesting collecting venue. Note that some units were very small. Amount of mail is unknown.
The following are UN Military actions with known Irish involvement and dates as of 1985:
UN TRUCE SUPERVISION ORG (UNTSO) 1958 - Present
UN EMERGENCY FORCE II 1973-1974
UN INTERIM FORCE IN LEBANON (UNIFIL) 1978- Present
UN INDIA-PAKISTAN OBSERVATION MISSION (UNIPOM) 1965-1985
UN OBSERVER GROUP LEBANON (UNOGIL) 6/1958-11/1958
UN OPERATION IN THE CONGO (ONUC) 1960-1964
UN PEACEKEEPING FORCE IN CYPRUS (UNFICYP) 1964-Present
Note that some missions ranged from 10 people upward.
REFERENCE: The Blue Helmets, The United Nations, 1985