this pool is there by design. On some mid-size and large USSR/Russian military ships which don't have a pool by design, you can find what your local building department would call "unpermitted remodeling" - as you can't really make a hole in a ship's deck floor (i mean theoretically you can, yet it would be a can of worms of totally different scale), the crew would build the pool up so there is only hardly a couple feet between the ceiling and the water and you get into it by climbing up the ladder.