This is the first time a submarine has been designated as a Class 4 submarine in Ireland.
It is an important step in the development of the Type 30 sub design, which was introduced in the 1960s to help provide a quick, safe and affordable alternative to the Type 31 diesel-electric submarine, which can travel at up to 40 knots.
The submarine, the Type 28, was commissioned in February 2016 and will be available to the Irish Navy from 2021.
Its design was based on the Type 26, a small, lightweight submarine which was first deployed to the Mediterranean in 1968.
The Type 28 was first produced in 1969, and has been sold to the Republic of Ireland, Canada, United Kingdom, the United States and Australia.
The Type 29 was built in 1973 and is currently being refurbished.
The Submarine Express will be an indigenous submarine for the Irish Army, with the Irish-built Type 29 already being used in some roles for the Royal Navy.
It will also be fitted with an advanced radar system, which includes a wide array of high-resolution sonar systems that can scan an area of a 200-metre radius and produce a 3D image of a target.
Its sonar can identify and locate targets on a 30-metres-wide surface, and can detect underwater targets as well as surface vessels.
The design will allow the submarine to carry out a wide range of missions.
The vessel will be capable of conducting intelligence and reconnaissance missions, including search and rescue, underwater surveillance and anti-submarine warfare.
The Irish Defence Forces is one of the world’s largest militaries, and is a partner in the UK’s armed forces.
It operates from the Clyde in Scotland, the Republic and Ireland.