In the Fall of 1965, it was decided that an existing facility of adjacent analog and digital computers would be up graded to provide hybrid computation capability. The Mermaid Monitor System, which provides the executive control functions and hybrid communications features, was developed in the very brief period during which the interface equipment was built. The initial version of Mer maid was written by digital systems programmers with no direct experience with analog computation who consulted with analog programmers with no digital or hybrid expe rience. Despite the general lack of knowledge and expe rience, the initial version was a workable monitor system which was used for over a year. Since the initial version of Mermaid was not an ideal monitor, a two-stage updating was undertaken to incor porate additional equipment and to strengthen Mermaid's capabilities in the area of hybrid inputloutput. On com pletion of this development cycle, the system will be com pletely disk oriented, and it will provide a maximum of convenience in programming for hybrid applications.