In case that the water-tight window is made of a parallel plane glass just as this lens, it is known that the spherical aberration and astigmatism don't change but chromatic aberration and pincushion distortion are generated in the periphery of the picture frame. This distortion is generated by the front parallel glass in principle and the degree becomes larger in proportion to the picture angle of the lens. As the situation can be checked when you look into a water tank, please try it if you have a chance to go to an aquarium. If you observe the inside scene of the water tank of which window is made of parallel plane glass, you will find that the inside scene is distorted and colored at the far side of the tank.
Because of that reason, regarding the lens wider than 35mm for "NIKONOS", separate lenses were prepared for use on land and underwater respectively such as "UW NIKKOR 28mm f/3.5 (exclusively for underwater)" and "LW NIKKOR 28mm f/2.8 (exclusively for on-land use)" (1983), for instance.
--Imaging.nikon.com: The birth of "W NIkkor 35mm f/2.5"