It transferred to the Territorial Force in 1908 as artillery support for the South Eastern Mounted Brigade.

It saw active service during the First World War in the Middle East, notably at Aden and in particular in the Sinai and Palestine Campaign, from 1915 to 1918.

Post war, the battery, along with A Battery, Honourable Artillery Company, was amalgamated with the City of London Yeomanry (Rough Riders) to form the 11th (Honourable Artillery Company and City of London Yeomanry) Brigade, RHA.

[2] The unit consisted of the battery and South Eastern Mounted Brigade Ammunition Column at Armoury House, Finsbury.

2nd Line units performed the home defence role, although in fact most of these were also posted abroad in due course.

[8] The 1st Line battery was embodied with the South Eastern Mounted Brigade on 4 August 1914 at the outbreak of the First World War and concentrated in the Canterbury area of Kent under Second Army of Central Force.

[11] The battery joined the division from Canterbury and attached to the 2nd South Midland Mounted Brigade.

In early April, the division starting leaving Avonmouth and the last elements landed at Alexandria before the end of the month.

By the middle of May, the horse artillery batteries were near Ismaïlia on Suez Canal Defences.

[12] On 14 July 1915, B Battery, HAC (along with Berkshire RHA and 28th Indian Brigade) left for Aden.

[16] They fought a sharp action at Sheikh Othman on 20 July that removed the Turkish threat to Aden for the rest of the war, before returning to Egypt.

In February 1916, the battery was rearmed with four 13 pounders and rejoined the Suez Canal Defences at Balla.

B Battery, HAC joined the division on formation and was assigned to XIX Brigade, Royal Horse Artillery (T.F.).

The battery, and its brigade, served with the Imperial Mounted Division in the Sinai and Palestine Campaign as part of the Desert Column.

The next day, a strong Turkish force attacked from the direction of Jisr ed Damiye and soon the artillery was in danger.

[30] It left Cupar on 10 May 1917 and proceeded to Heytesbury, Wiltshire where it joined CXXVI Brigade, RFA.

[29][e] 2/1st Warwickshire RHA, by now also rearmed with 18 pounders, proceeded to France on 21 June 1917 and joined the brigade there.