I doubt that it would be an underwater lens. But can't underpin that believe with reasons.
The fact that the lens is large and heavy doesn't speak against it. People are doing more going underwater than scubadiving along a reef to take holiday snaps.
Allowing water into the lens would eliminate pressure problems, which would otherwise require a rather sturdy construction. However, unless you also flood the film or sensor, you will have to have a water barrier at some point. And no better place than at the front end of the optical system (i.e. the front lens), no worse point than somewhere between the lens and the film/sensor.
That water reduces the refractory index is a given you have to deal with anyway when submerging a camera, AgX. You have to design a lens with that in mind.
The differing refractive index at different depths and salinity would be a bigger problem in a fixed design lens.
A bare barrel like this one would appear not to be the whole deal. It is obviously meant to be mounted inside something else, to be pat of a bigger apparatus. And that something else will do a fine job keeping the dark inside. So i wouldn't worry about the wholes from that respect.
But i still think it is a projection lens.