The Naval Service will more than halve the age of its eight-vessel fleet when the third ship in a €162m order is delivered by 2016.
The news came as the Navy's second new vessel, LE James Joyce, is now concluding sea trials and will be delivered within weeks for commissioning in May.
A sister ship to the LE Samuel Beckett which was delivered last year, LE James Joyce was built at Babcock Marine's shipyard in north Devon.
A third vessel, the order for which was confirmed by Taoiseach Enda Kenny, is now under construction and is scheduled for a late 2016 delivery.
The delivery of the as-yet-unnamed third offshore patrol vessel will dramatically reduce the age profile of the navy's Haulbowline-based fleet.
Literary
The vessel, like its sister ships, is expected to be named after an Irish literary figure.
The third new vessel will see five of the navy's main patrol vessels having entered the fleet since 1999.
At a cost of €54m each, the new vessels are the most hi-tech ever operated by the Naval Service and are capable of handling advanced technology such as drones and robotic submarines.
The LE Samuel Beckett replaced the 35-year-old LE Emer which was sold at auction in October 2013 to an African consortium.
The LE James Joyce will replace the LE Aoife (1979) which was decommissioned last January and has now been donated to the Maltese navy.
Each of the new ships are developments of the original design chosen for the LE Roisin/LE Niamh in 1997.
Naval Service officials confirmed that the new ships will dramatically increase the technological capacity of the Navy both in terms of surveillance and incident response times.
The ability to operate drones, which are already used by the Defence Forces, will also dramatically increase the navy's patrol and surveillance capabilities.
Each ship can similarly operate remotely controlled mini- submarines.
The new vessels are 12m bigger at 90m in overall length than the old LE Roisin/Niamh design. With a top speed of 23 knots, the new ships will also be over 30pc faster than the ageing vessels they replace.
The Government has insisted the deal represented exceptional value for money with shipyards offering cut-price contracts as they battle for orders.
obsolete
Defence minister Simon Coveney warned that Ireland cannot afford to revert to the "bad old days" of the 1940s and '50s when the Naval Service was totally reliant on a fleet of ageing and obsolete former Royal Navy corvettes. It is expected that the third new ship will replace LE Aisling (1980), which will have seen 36 years of service.
When all three are commissioned, the oldest ship in service will then be the LE Eithne (1984).
LE Eithne will also be the only remaining vessel in the fleet which was built in Ireland.
The three craft are the first new ships commissioned for the Naval Service since the LE Roisin (1999) and LE Niamh (2001) which displace 1,500 tonnes.