British troops did operate on the Eastern Front during WWI, though only a single unit. This was the a squadron of the Royal Naval Air Service (RNAS) Armoured Car Division (yes, that is the Navy's Air Force's Army).

The RNAS had been at the forefront of British armoured car development. Their first vehicles had been improvised from civilian cars, to help with the RNAS' role of scouting for the Royal Marine Division during the defence of Antwerp in late 1914. This experience, combined with the fact that the RNAS was funded outside the usual channels for naval funding, led to an expansion and formalisation of the RNAS Armoured Car units. By March 1915, a Division of fifteen twelve-car squadrons had been formed (though five of the squadrons used motorcycles instead). However, by the time the cars started to enter service, their utility on the Western Front was limited. The end of manoeuvre warfare and the rise of trench warfare meant that the cars had no place on the Western Front. Instead, they were used in peripheral theatres, with squadrons fighting during the Gallipoli Campaign, during the campaigns against German East and West Africa, and in the deserts of Egypt and the Arabian Peninsula. In August 1915, the RNAS Armoured Car Division was disbanded during a reorganisation of the RNAS, with most of the cars being handed over to the Army. One squadron, though, would remain under naval control. It was this squadron that would serve in Russia.

The squadron (No. 1 Squadron) operated in Flanders until October 1915. After this, it returned to Britain, to prepare for deployment to Russia. The Eastern Front was much more open than the Western Front, with manoeuvre warfare still occurring, making it much more suitable for the armoured cars. No. 1 Squadron was shipped to Archangel in June 1916. After this, it was brought to Vladikavkas by rail. From Vladikavkas, it joined the Russian Army around Erzurum to fight against the Ottomans, involving long journeys across country without paved roads. After a period of operating around Erzurum, the squadron was shipped to Romania via Odessa. In Romania, it participated in the retreat from Dobrudja. In the summer of 1917, it took part in the Kerensky Offensive in Galicia. This was its last operation before returning home. When it returned to Britain, the unit was disbanded, and the cars given to the Army.

No larger units were sent to Russia (though a division of British submarines did operate in the Baltic). This was largely because of a lack of units to send. The British and French armies were heavily committed to the Western Front. Units could rarely be spared for peripheral operations - a considerable number of RN plans for attacks against the coast of Germany or German-held Flanders had to be cancelled due to the lack of available troops. The one time significant numbers of troops were available, they were committed to the Gallipoli campaign, to help break the deadlock created by the failures of the Allied navies to defeat the Ottoman defences of the Dardanelles.