She was the former Royal Navy ship HMY Helga and was involved in shelling Liberty Hall in Dublin from the River Liffey with her pair of 12-pounder naval guns[3] during the Easter Rising of 1916.

The prefix was introduced in December 1946 when the Irish Naval Service was established with the purchase of three corvettes from the Royal Navy replacing Muirchú.

At this time the "II" was dropped from her name and she served as an anti-submarine patrol vessel as well as undertaking escort duty in the Irish Sea.

She was later used to transport Royal Irish Constabulary special constables known as Black and Tans around the coast when many of the roads in Ireland were rendered impassable by the IRA in the War of Independence.

Muirchú was sold to Hammond Lane Foundry by the Irish Government, and while on passage to Dublin on 8 May 1947 she sank off the Saltee Islands – though not before her crew safely evacuated.