Seeing the success of UAVs, a DoD-funded lab started working on autonomous unmanned underwater vehicles. Building on their previous work, they outfitted their first AUV with a machine learning-based AI, solar panels and an experimental weapon that heats water to near-plasma. During the first field test, the tether was mysteriously cut (later examination suggested a high heat source was the culprit) and their AUV disappeared. They assumed it sunk to the bottom, but it didn't...

Strength
Marino was deployed near a navy base and quickly learned to adapt it's behavior to military-level ships and personnel. It is able to calculate an optimal trajectory and engine cutoff times to approach any craft without being detected.

Strength Source
Experimental heat-based weapon and reactive and learning AI.