Aquaman issue #1 1991

In Aquaman (Volume 4) #1, the domed city of Poseidonis is under siege by a fleet of submarines from the sovereign nation of Oumland. The attacks cause repeated bombardments, eventually cracking the city’s dome. Meanwhile, Aquaman is in Newport Beach, California, helping locals move a beached whale — a creature he senses has been traumatized by the death of her calf. The local sea life is acting strangely, hinting at deeper disturbances  

Back in Poseidonis, King Thesily convenes an emergency council with Lord Vulko and Minister F'ancha. The session is interrupted when Oumlandian shock troopers breach the dome. In Oumland, the Prime Minister meets with a disguised Black Manta, who urges the start of a retaliatory strike against Atlantis