The aim of this study was to contribute to the knowledge of Total Systems theory and methodologies, by developing an aid to decision making on the effectiveness of complex man-machine organisations. Sponsored by the Ministry of Defence (Navy) as a collaborative research project, the study was to be based on Royal Navy ships and also linked with certain MOD(N) projects working on related effectiveness problems. Initial pre-feasibility, then feasibility studies established a simple model of Effectiveness as the combination of Availability, Performance and Human Factors, which was followed by a more thorough examination of the Availability Function. The development of an Information System designed for the collection and analysis of reliability and maintainability data was central to this phase of the research. This culminates in a comprehensive description of the Phase I hardware, software requirements and information distribution network to be installed and operating commencing in 1983. The Human Factors research was linked to two additional Ministry of Defence (Navy) projects who made available the Human Factors data. This data, collected from five ships of the Type 42 Guided Weapons Destroyer Class, was concerned with the Operations Room organization. Using this data base, a subjective analysis resulted in key indicators being produced which were used with a rating scale technique to develop profiles. Following a systemic overview three interactive indicators - Variable Disjunction of Information, Knowledge and Information Processing were used as the basis of an Information Transfer Function conceptual model. This model, when combined with Systems Interaction Diagrams enabled a Methodology to be designed which was evaluated against a three man-function element within a total Operations Room complement of 33 men. On the premise that the Human Factors function could be transformed to metric data the framework of a Human Factors model was developed, based on an existing Total Ship Availability Model with the potential that these could be combined to produce an Effectiveness model. The information System, the proposed Methodology and the framework of a Ship Effectiveness Model were then incrementally and theoretically linked in order to develop the organisation of a decision making aid for evaluating the effectiveness of complex man-machine systens. The research was not intended to test or validate the decision making aid, as aspects of this will need to be approved by Ministry of Defence (Navy) authorities before proceeding to the next phase of implementing the results so far produced.