Board Thread:Game Updates/@comment-1820055-20151105024044/@comment-26574811-20151118121545

10▼新しい敵「PT小鬼群」について 秋イベの期間限定海域では、新しい敵艦「PT小鬼群」が登場します. 彼女たちには、戦艦等の大型艦艇の攻撃はあまり有効ではありません. 駆逐艦等の小型艦艇が有効です. ※大型艦艇も、「副砲」を装備することである程度対抗することも可能です.

New enemy :PT group

somewhat immune to large caliber fires, but can be effectively eliminated by smaller guns, including DD guns or secondary guns from larger ships.

By the way, I think this is the first time the devs treated the Abyssals as human-like creatures. They said " 彼女たちには", which means "to them(human female plural)"