Complex sentence: Georgiou joined the British Army, and served, at first with distinction, in 1st Battalion, Parachute Regiment in Northern Ireland, credited as one of the best marksmen in the unit.
Split into simpler sentences: Georgiou joined the British Army and served, at first with distinction, in 1st Battalion, Parachute Regiment in Northern Ireland. He was credited as being one of the best marksmen in the unit.