One of my older concepts made fresh.

This centuries old piece of sadistic axis engineering, employs an infant, grated to an experimental submarine cutter, and mobile radiostation. Driven mad by decade after decade of agony and solitude.
It does not know what it is, It knows no language, only a set of automatic responses. It is uncertain when it was developed, or how it was released.
Its telltale method of approach is to emit a shortwave radiosignal at an intruding submarine, a series of ominous tunes, followed by a short series of numbers in german. If a corresponding code is not transmitted back it will attempt to sink the submarine by cutting rectangular holes in its plating. Several submarines of mixed origin are theorized to have been compromised by this hellish contraption.