In Brief: Submarine Reflection was Sailor Neptune's second attack in the anime and her first attack that used her Talisman, the Deep Aqua Mirror.

While the mirror could show Neptune visions of the future on it's own, when used in the Submarine Reflection attack it could be used to reveal more information in targets as seen in the the Sailor Moon SuperS movie, Black Dream Hole or even release powerful energy blasts at them as shown in Episode 169 of Sailor Stars.

Cultural: The Deep Aqua Mirror is in fact based on a real world treasure called the Yata no Kagami which makes up one third of The Sacred Treasures of Japan.

This mirror represents honesty and wisdom, making for a perfect inspiration for the character of Sailor Neptune.

The Attack: Submarine Reflection doesn't have the traditional stock animation sequence like so many of the other attacks do, instead on the few times it was used it was done in real time against a stylised background.

Sailor Neptune would hold out her mirror and it would begin to glow. She would pull the mirror back and then release it's power.