The 1st Battalion deployed to South Africa as part of 5th (Irish) Brigade, commanded by Major-General Fitzroy Hart, and saw action at the Battle of Colenso in December 1899, part of the attempt to relieve the town of Ladysmith, besieged by Boer forces. The brigade suffered heavily during their participation in the battle, the Boers inflicting heavy casualties: the regiment had 24 men killed and 105 officers and men wounded. The Rangers fought at Spion Kop in January 1900 and the Tugela Heights in February 1900 during further attempts by General Sir Redvers Buller to relieve the besieged town of Ladysmith. In late February the siege of Ladysmith finally came to an end after it was relieved by British forces. The 1st Battalion returned to India in 1903.