The 90m-long vessel has been named HMS Medway and is expected to enter service with the Royal Navy in 2019.
HMS Medway is named after the River Medway in Kent and was built by BAE Systems.
The five new OPVs are set replace the navy’s current River-class patrol ships, including HMS Tyne, HMS Mersey, HMS Severn and HMS Clyde.
UK Defence Secretary Sir Michael Fallon said: “This year we have already named our second aircraft carrier, two Type 26 frigates and the first in the Offshore Patrol Vessel class.
“It is a privilege to see yet another ship named for the growing Royal Navy.
“Named after Kent’s main river, my family has taken a particular interest in HMS Medway over the course of its construction and this is a proud day for all involved.
“From counter-terrorism and anti-smuggling to securing the UK’s borders, HMS Medway will help keep Britain safe.”
HMS Medway has been designed to meet the Royal Navy’s counter-terrorism and anti-smuggling requirements in order to safeguard the nation’s borders and shoreline.
The first of class, HMS Forth, is currently undergoing trials off the Scottish coast. The remaining three vessels will be known as Trent, Tamar and Spey.
Each River-class vessel can accommodate a crew of 58 personnel and is equipped with a 30mm main gun, as well as a flight deck capable of accommodating a Merlin helicopter.
The new Batch 2 River class OPVs can travel at a top speed of 24k and are able to sail more than 6,300mi without resupply.
All five vessels are expected to enter service with the navy before the end of 2020.