The Steyr Armee Universal Gewehr (AUG) meaning Army Universal Rifle entered service with the Defence Forces in 1988 replacing the FN Rifle. It fires a NATO standard 5.56mm round. The weapon is of a ‘bullpup’ design which means the mechanism and magazine are located behind the trigger and pistol grip which reduces the overall length of the weapon without reducing the length of the barrel. The Steyr AUG is manufactured in Austria and is in service with many forces across the world such as Austria and Australia. In 2014 the Defence Forces began a modernisation programme to upgrade the Steyr AUG A1s. The upgrade included a complete refurbishment of the weapon and the addition of a long Picatinny Rail along the top of the housing group, and the introduction of a Trijicon Advanced Combat Optical Gunsight (ACOG) with 4x magnification. The Mod 14 variant offers greater accuracy and the flexibility to add laser light modules for target designation and discrimination, night vision and thermal weapon sights, white light lamps etc. The upgrade has greatly extended the lifespan of the weapon.

The attached clip from RTÉ Archives from March 1987 captures part of the selection process used to replace the FN Rifle.
https://www.rte.ie/archives/collections/news/21242662-army-test-weapons/