From "An Abbreviated History of the Bolo":

The first completely automated Bolo, designed to operate normally without a man on board, was the landmark XV Model M. This model, first commissioned in the twenty-fifty century, was widely used throughout the Eastern Arm during the Era of Expansion and remained in service on remote worlds for over two centuries, acquiring many improvements in detail while remaining basically unchanged, through increasing sophistication of circuitry and weapons vastly upgraded its effectiveness.

The always-present, through perhaps unlikely, possibility of capture and use of a Bolo by an enemy was a constant source of anxiety to military leaders and, in time, gave rise to the next and final major advance in Bolo technology: the self-directing (and, quite incidentally, self-aware) Mark XX Model B Bolo Tremendous.

The Mark XX was greeted with little enthusiasm by the High Command, who now professed to believe that an unguided-by-operator Bolo would potentially be capable of running amok...