However, on the outbreak of war on 4 August 1914, many members volunteered for Imperial Service.

Therefore, TF units were split in August and September 1914 into 1st Line (liable for overseas service) and 2nd Line (home service for those unable or unwilling to serve overseas) units.

[6] By March 1916, the brigade was at Dunbar, East Lothian.

[3][a] In July 1917, 2/1st Lothians and Border Horse moved to Haddington.

2/1st Ayrshire was stationed at Omagh, County Tyrone,[9] the 2/1st Lanarkshire at Derry,[10] and the 2/1st Lothians and Border Horse at Londonderry and Enniskillen, County Fermanagh.