HMS Tamar is a Batch 2 River-class offshore patrol vessel of the Royal Navy. Named after the River Tamar in England, this is the seventh Royal Navy ship to be named Tamar. She is the fourth Batch 2 River-class vessel to be built and is forward deployed long-term to the Indo-Pacific region with her sister ship HMS Spey.

The British Indian Ocean Territory (BIOT) is an Overseas Territory of the United Kingdom situated in the Indian Ocean, halfway between Tanzania and Indonesia. The territory comprises the seven atolls of the Chagos Archipelago with over 1,000 individual islands, many very small, amounting to a total land area of 60 square kilometres. The largest and most southerly island is Diego Garcia, 27 square kilometres, the site of a Joint Military Facility of the United Kingdom and the United States. Official administration is remote from London, though the local capital is often regarded as being on Diego Garcia.