This is a bowl shaped like a spherical naval mine.
Munktiki Imports produced these in a blue or a gray glaze.
These naval mines were self-contained explosive devices placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines were deposited and left to wait until they were triggered by the approach of, or contact with, any vessel. The nubs around the spherical body are termed "Hertz horns" (maybe because if you touch them it hurts?).