An attack on Saturday near the eastern oil hub of Brega is the second by the choppers based on the ship HMS Ocean, which is docked off the north African coast, following their first mission on Friday.
"At sea, HMS Ocean launched her British Army Apaches against a multiple rocket launch system positioned on the Libyan coast near Brega," Major General Nick Pope, spokesman for the Chief of Defence Staff, said in a statement on Sunday. "The attack helicopters used Hellfire missiles to destroy their target before returning safely to the ship."
British Tornado strike planes separately joined other NATO aircraft in a "major strike on a large surface-to-air missile depot" in the Libyan capital Tripoli, Pope added.
British aircraft have attacked more than 410 regime targets as part of the NATO campaign to enforce a UN Security Council resolution passed in March to protect Libyan civilians, he said.
On Friday night British Apaches destroyed a radar station and a military checkpoint in their first mission over Libya since British Prime Minister David Cameron approved their use late last month.
French attack helicopters also operated over Libya for the first time.
British Foreign Secretary William Hague met Libyan rebel leaders in their stronghold of Benghazi on Saturday, while Russia's top diplomat warned the NATO operation in Libya was "sliding towards" a land campaign.