HMS Liverpool left Portsmouth this morning to go to Libya.
The Type 42 destroyer has been sent to the warzone to help enforce the NATO naval blockade as part of Operation Unified Protector.
She will replace Type 22 frigate HMS Cumberland which is being sent back to Britain to be decommissioned after more than a month in Libya.
Liverpool, which has a crew of around 280, joins Portsmouth-based frigate HMS Westminster, in the Mediterranean.
A navy spokesman said: ‘Liverpool left this morning and she will be relieving Cumberland over the course of the next month.
‘She will be conducting embargo patrols.’
Last month, Portsmouth-based destroyer HMS York was also sent to Libya. But she was relieved by Westminster to continue on to patrol the Falkland Islands.
Eleven nations have deployed naval forces into the central Mediterranean so far in support of Operation Unified Protector.
The purpose of the operation is to protect civilians and civilian-populated areas under threat of attack.
The aim of the naval blockade is to stop arms entering the country and also to keep Colonel Gaddafi’s warships holed up in port.
Prior to coalition forces getting involved in Libya, Gaddafi’s warships had reportedly launched strikes on civilian rebels from the sea.
News of Liverpool’s departure came as delegates from across the world arrived in London to lay out Libya’s post-Gaddafi future should the dictator fall in at the hands of rebel forces.
Pro-Gaddafi forces have been pushed back towards the west the country by rebels in the past week thanks to air raids from international forces.
But government forces stopped a rebel assault on Gaddafi’s hometown of Sirte today.
Reports say rockets and tank fire sent Libya’s rebel volunteers in a panicked scramble away from the front lines, suggesting that the opposition is still no match for the superior firepower and organisation of Gaddafi’s forces, despite support from international airstrikes.