Ace uses Orbital Interceptor to swim underwater with Max.
First appearance of the Skybolt and Detonator weapon systems.
Although never suggested, rumours persist that the sealab featured in this episode is none other than the one from the classic "sealab" cartoon. Since Centurions and Sealab were both created by Hanna-Barbera, it is a distinct possibility. Then again it could be an "in-joke" by the writers..
In true Star Trek tradition, Skyvault can't beam through Sealab's shields.
It is unlikely that Orbital Interceptor was suitable for submersible operation. Submarines are built to withstand pressure much greater on the outside, while orbital vehicles are expected to withstand pressure working form the inside, in the reverse direction. Building a system that could function in both environments would be an engineering nightmare, if not impossible.