a special forces unit, the Special Boat Service. Escort fleet The escort fleet comprises guided missile destroyers and frigates and is the traditional workhorse of the Navy. there are six Type 45 destroyers and 12 Type 23 frigates in active service. Among their primary roles is to provide escort for the larger capital ships—protecting them from air, surface and subsurface threats. Other duties include undertaking the Royal Navy's standing deployments across the globe, which often consists of: counter-narcotics, anti-piracy missions and providing humanitarian aid. The Type 45 is primarily designed for anti-aircraft and anti-missile warfare and the Royal Navy describe the destroyer's mission as "to shield the Fleet from air attack". They are equipped with the PAAMS (also known as Sea Viper) integrated anti-aircraft warfare system which incorporates the sophisticated SAMPSON and S1850M long range radars and the Aster 15 and 30 missiles. 16 Type 23 frigates were delivered to the Royal Navy, with the final vessel, , commissioned in June 2002. However, the 2004 Delivering Security in a Changing World review announced that three frigates would be paid off as part of a cost-cutting exercise, and these were subsequently sold to the Chilean Navy. The 2010 Strategic Defence and Security Review announced that the remaining 13 Type 23 frigates would eventually be replaced by the Type 26 Frigate. The Strategic Defence and Security Review 2015 reduced the procurement of Type 26 to eight with five Type 31e frigates to be procured. Mine countermeasure vessels (MCMV) There are two classes of MCMVs in the Royal Navy: three s and six s. The Hunt-class vessels combine the separate roles of the traditional minesweeper and the active minehunter in one hull. If required, the Sandown and Hunt-class vessels can take on the role of offshore patrol vessels. Offshore patrol vessels (OPV) A fleet of eight River-class offshore patrol vessels are in service with the Royal Navy. The three Batch 1 ships of the class serve in U.K. waters in a sovereignty and fisheries protection role while the five Batch 2 ships are forward-deployed on a long-term basis to Gibraltar, the Caribbean, the Falkland Islands and the Indo-Pacific region. The vessel MV Grampian Frontier is leased from Scottish-based North Star Shipping for patrol duties around the British Indian Ocean Territory. However, she is not in commission with the Royal Navy. In December 2019, the modified Batch 1 River-class vessel, , was decommissioned, with