The first of the Royal Navy's new offshore patrol vessels (OPVs) has been officially named at a ceremony in Glasgow.

The 90-metre warship will be known as HMS Forth after being given its title at the BAE Systems Scotstoun shipyard on Thursday.

She will soon depart on sea trials before beginning service in 2018.

HMS Forth is the first of a fleet of five new batch 2 river-class OPVs being built on the Clyde, which are all expected to be in service by 2021.

The warship, which will be used for counter-terrorism, anti-smuggling and maritime defence duties, was named by the Lady Sponsor Rachel Johnstone-Burt.

She kept naval tradition by breaking a bottle of whisky on the ship's bow.

Harriett Baldwin, minister for defence procurement, said: "As part of a sustained programme delivering world-class ships and submarines, HMS Forth's naming is a vitally important part of the government's ten-year £178bn plan to provide our Armed Forces with the equipment they need.

"From counter-narcotics operations in the Caribbean, to securing the UK's borders on patrols closer to home, the Royal Navy's new offshore patrol vessels will help protect our interests around the world."

HMS Forth, the fifth Navy vessel to bear the name, is affiliated with the city of Stirling after it adopted a ship of the same name during the Second World War.

Defence bosses say work on HMS Forth and her sister ships is sustaining about 800 Scottish jobs.

The vessel is equipped with a 30mm-calibre cannon and flight deck capable of accommodating a Merlin helicopter and manned by a crew of 58 sailors.

Admiral Sir Philip Jones, first sea lord and chief of naval staff, said: "In a few short years, these five offshore patrol vessels will be busy protecting the security of UK waters and those of our overseas territories.

"They are arriving in service alongside a new generation of attack submarines and fleet tankers, and will be followed shortly by new frigates and other auxiliaries; all of this capability will coalesce around the Queen Elizabeth-class carriers."

The Ministry of Defence (MoD) has invested £648m in the OPV programme, which is one of the commitments in the strategic defence and security review 2015.

Vice-admiral Simon Lister, chief of materiel (fleet) for the MoD's defence equipment and support organisation, said: "The naming is a significant milestone in the life of HMS Forth and in the wider offshore patrol vessel programme, which is well on track to deliver all five of the new ships by the end of 2019."