Assault on Vectes
Three (two big, one small) attacked the towns of New Jacinto and Pelruan resulting in the First Battle of New Jacinto and the Battle of Pelruan. During the battles, the Leviathans released hundreds of polyps at the two towns in attack before the smallest Leviathan was killed by all the ammo of a King Raven chopper being released into its head, the second one being killed by a combined torpedo attack from the vessels Zephyr and the CNV Clement and the last one being killed by the Hammer of Dawn after being lured into a trap by Delta Squad. The first two to die exploded when killed, but the last one beached and it is unclear whether or not it exploded.
A fourth Leviathan attacked causing the Second Battle of New Jacinto. This one didn't release any polyps although it had at least a few and concentrated on attacking. The Hammer of Dawn failed twice to kill it and then went offline and the gun batteries of New Jacinto and two King Ravens also failed to harm it. A depth charge ruptured its eardrums and forced it to the surface where Marcus Fenix threw a grenade down its throat, blowing it up. A few polyps survived on a chunk of the Leviathan, but Bernadette Mataki killed them with a Longshot and well-aimed detonations.
Sinking of the Sovereign
Later, during a Lambent attack on the Raven's Nest Class ship CNV Sovereign, a huge Lambent Leviathan, twice the size of the ones previously encountered engaged the ship, catching the COG off guard. It was first encountered when it reached inside one of the Raven platforms, crushing the Raven on it and releasing tonnes of polyps. Delta shot the tentacle making the beast retreat. Later on the deck, the beast reared up out of the water and bit down on the deck, causing it to crack open making Delta fall into the engineering deck. After they navigate through engineering, they come up against the beast again as it bites clean through the deck.
After it retreats once more, Marcus Fenix and the rest of his team made their way to the Silverbacks on the ship and attempted to hold the Leviathan off while Augustus Cole's team came up with an idea to get rid of it from on top of Centennial Bridge. Damon Baird came up with a plan to drop Tickers onto the Leviathan and after fighting their way to a Ticker cage, they kicked the Tickers onto the Leviathan's head and caused the beast to explode. The explosion destroyed the Sovereign and a tentacle strike collapsed the Centennial Bridge where Cole, Baird, Clayton Carmine and Samantha Byrne were. Its remains scattered all over the Hanover coast. Any other Lambent Leviathans were wiped out when the Imulsion Countermeasure Weapon was activated at Azura.