The invention of the tank during World War One virtually sealed the fate of all British cavalry regiments as it became apparent that the tank was the future of mobile warfare. Many cavalry regiments with long histories traditions were either amalgamated or disbanded after World War One in the massive programme of demobilisation. The 5th Royal Irish Lancers were one of the latter being disbanded in 1921 along with many other cavalry regiments of the British Army. The 5th RIL seem to have been luckier than some other regiments however and were not disbanded for long, being reintroduced in 1922 and amalgamated with 16th Lancers in the same year.
This new regiment known as the 16th/5th Lancers whose motto was “Aut cursu, aut cominus armis” means "Either in the charge, or hand to hand". The numbering of the regiment seems a little strange but this is due to the 58 years of non-existance of the 5th RIL from 1799 - 1857, precedence being given to the 16th Lancers. The remnants of the 5th Royal Irish Lancers Regiment in 1922 provided the establishment for D Squadron of this new regiment.
The 16th Lancers, like the 5th Royal Irish Lancers, had a proud tradition going back as far as 1759. The 16th Lancers forged this tradition having served in the American War of Independence, India, Afghanistan, The Peninsula Wars, and The Napoleonic Wars including Waterloo, The Boer War and The Great War.
Had it not been for the temporary disbandment of the 5th Royal Irish Lancers in 1799 it is a pretty safe bet that they would have gained more battle honours in the Peninsula Wars, Napoleonic Wars, and Crimean Wars, however this was not to be.
The 16th/5th Lancers went on to achieve more battle honours during World War Two however this time the horses, lances and mass cavalry charges had been replaced with Matilda and Valentine tanks, 6-Pounder Guns, high explosive shells, armour piercing shells and machine guns.
As part of 6th Armoured Division they fought in the following battle with distinction:

North Africa 1942-43

Kasserine
Fondouk
Kairouan
Bordj
Djebel Kournine
Tunis
Bromballa
Bou Ficha

(in 1943, their Matilda and Valentine tanks had been replaced by Sherman Tanks)

Italy 1944-45

Monte Cassino II
Liri Valley
Monte Piccolo
Capture of Perugia
Arezzo
Advance to Florence
Argenta Gap
Traghetto,

The regiment's active service did not end there, they were soon to see action in Egypt in 1948. During the 1960s they served in Germany, Aden, Bahrain and Hong Kong.
In the 1970s they saw active service in Northern Ireland and in Cyprus (1974) and the Gulf War in 1991.
The 16th/5th were to go through another restructuring programme in 1993 which saw them amalgamated with the 17th/21st Lancers to become the Queens Royal Lancers. Within The Queen's Royal Lancers the 5th Lancer Squadron is the direct descendant of the original 5th Royal Irish Lancers.
Most recently the Queens Royal Lancers served in The Gulf War II.