In July 1917 the Royal Navy needed shallow-draught minesweepers - vessels that could work harbour mouths, river estuaries, anywhere the deep-water sweepers couldn't reach. Someone noticed that the War Department was already building exactly the right kind of boat: tunnel tugs for river operations in Mesopotamia, where the British army was fighting the Ottoman Empire on the Tigris and the Euphrates. The Navy bought six of these tugs that October and another four in December. Ten boats, built for the Iraqi rivers, were converted into minesweepers and based at Dunkirk in 1918 to work the Flanders coast. One of them, ET 10, came from the Lytham Shipbuilding and Engineering Company in Lancashire. In April 1919 she was reassigned with three sisters - to a war no one had quite declared - and given the name Sword Dance.

The Russian Civil War had been running since 1917, and the Allied powers, still officially at war with Imperial Russia's former enemies until 1918, had landed troops at Archangel and Murmansk to support the White Russians against the Bolsheviks. The intervention was unpopular at home, of dubious legal standing, and increasingly a holding action - an attempt to keep the front intact long enough to evacuate. The Royal Navy was tasked with operations on the Northern Dvina, the great river that empties into the White Sea at Archangel. Sword Dance was prepared for the deployment: minesweeping and minelaying gear installed, sides boarded up for the Arctic weather, heaters fitted to warm aircraft engines in the cold, and mosquito netting for the swarms of insects that came with the brief subarctic summer. She mounted a single six-pounder gun. Then she was towed to the Arctic - she could not make the passage under her own power.

Sword Dance arrived at Yukanski - now Ostrovnoy in Murmansk Oblast - on 7 June 1919. She joined three sister sweepers and the monitor HMS Humber on the river. A considerable force had been assembled: six monitors, six river gunboats, the four sweepers. The Northern Dvina runs north from Kotlas in the interior to the White Sea, and the river was the spine of the British advance. But the river was too shallow in places for most of the force to reach the front line. Only the sweepers - with the shallowest draught of any vessel - could reach as far as Kotlas itself. On 20 June 1919, British and White Russian forces under General Edmund Ironside launched an attack to capture Bolshevik positions at Topsa and Troitsa. The Bolsheviks counterattacked the next day; the gunboat broke the attack with artillery fire.

On 24 June, Sword Dance was stationed on the Dvina near Troitsa when crew noticed that some of the markers indicating the swept channel had been moved. The minesweeper put out to relay them. While doing so, she struck a mine, perhaps moved deliberately, perhaps drifted by the current. She sank in shallow water, her bridge and stem still showing above the surface. One crew member died. Lieutenant Alan Halliley, the commanding officer, was wounded. Salvage was attempted, but the withdrawal of British troops from North Russia was already underway and the effort was abandoned. On 17 September 1919, what was left of Sword Dance was blown up where she lay. Halliley received the Distinguished Service Order for his service in North Russia. His first lieutenant, Sub-Lieutenant Archibald Dunn, received the Distinguished Service Cross. The intervention ended within weeks. The Bolsheviks won the civil war. Sword Dance had been built to clear rivers in Mesopotamia and died clearing a river half the world from there.