The only British forces operating in Russian territory during WWI were under the command of the Admiralty: the Russian Armoured Car Division of the Royal Naval Air Service (RNAS) and RNVR (Royal Navy Volunteer Reserve), and a flotilla of submarines in the Baltic. The submarines arrived in Russia from 1915, while the armoured cars were shipped to Russia in early 1916. Both forces served until the Russian Revolution, being removed in the aftermath.

One of the most important sources of iron ore available to the Germans was the mines at Lulea in Sweden. Ore from these mines were shipped south through the Baltic. The British wished to intercept these ships, a task beyond the capabilities of the Russian Navy. To bolster them, several British subs were deployed to the Baltic. Six of the modern E-class submarines made the journey through the Kattegat. This was a tricky journey, patrolled by German vessels and riddled with sandbanks and shallow water. One of these subs, E13, ran aground in the Oresund, where she was sunk by a German warship. Four older, smaller C-class coastal subs were also deployed. However, these didn't have the range to travel from the UK to Russia's Baltic ports. Instead, they were towed around Norway to Archangel. From here, they were taken to St Petersburg by river barge. The Baltic submarine flotilla saw sterling service against German shipping. Based from Reval (now Tallinn), they sank several merchants and the cruiser Undine and damaged the battlecruiser Moltke. Two submarines were lost: E18 was sunk in 1916, most likely by a mine, while C32 was stranded in 1917 during the German invasion of the Moonsund Islands. Following the Russian Revolution, the treaty of Brest-Litowsk forced them to retreat to Helsinki. However, in 1918, they were scuttled after the Germans intervened in the Finnish Civil War.

The Royal Navy, and particularly the RNAS had been a front-runner in the development of armoured cars. The RNAS saw them as a way to protect its airfields, recover downed aircrew and secure lines of communication. RNAS armoured cars made several raids and ambushes against German forces on the Western Front. They also participated in the Gallipoli campaign and in South West Africa. Moving into 1916, the declining need for armoured cars on the Western Front and worries about Russian capabilities meant that it was decided to deploy a force of them to Russia, with most of the remainder being transferred to the Army. Three squadrons of armoured cars were combined to form a division (albeit one that was much smaller than the typical army division). Unlike previous armoured car units, this came under the auspices of the RNVR rather than the RNAS, though most of the personnel were the same. The Armoured Car Division was shipped to Murmansk and fought on several fronts. They initially fought against Turkish forces in the Caucasus, but moved to the Romanian front in late 1916. Here, they fought Bulgarian and German forces. In 1917, they supported the July/Kerensky Offensive, the last gasp of the post-revolutionary Provisional Government. However, with the political situation becoming more precarious, they were withdrawn to the UK in September.