Automatic systems implement simple mechanical functions that constitute a response to the environmental stimuli. Automated systems are more complex, because they shape their behaviours not only based on environmental stimuli, but they also take into account the previously defined rules. On the other hand, autonomous systems have the ability of self-direction, which does not result directly from the implemented software. Therefore, they are also able to shape their behaviour through the ability to self-learn. An interesting view on this issue is presented by A. Williams. He points out that in principle we should talk about the functions implemented by the combat system, which are performed in an automated or autonomous manner. According to him Autonomous functioning refers to the ability of a system, platform, or software to complete a task without human intervention, using behaviours resulting from the interaction of computer programming with the external environment. Tasks or functions executed by a platform, or distributed between a platform and other parts of the system, may be performed using a variety of behaviours, which may include reasoning and problem solving, adaptation to unexpected situations, self-direction, and learning. Which functions are autonomous – and the extent to which human operators can direct, control, or cancel functions – is determined by system design trade-offs, mission complexity, external operating environment conditions, and legal or policy constraints. This can be contrasted with automated functions, which (although they require no human intervention) operate using a fixed set of inputs, rules, and outputs, the behaviour of which is deterministic and largely predictable. Automatic functions do not permit the dynamic adaptation of inputs, rules, or outputs.
To sum up, it seems impossible to define a precise boundary between autonomous, automatic or automated weapon systems. Moreover, individual degrees of autonomy within the presented aspects may remain in multithreaded relations to each other. Simply put, at one end of the scale there are simple elements acting on the principle of stimulus-reaction, while on the other end there are complex systems capable of learning and drawing conclusions based on information obtained from the environment, in which they function. The distinguishing characteristic is the ability to adapt, independence in functioning and system’s ability to independently make decisions. The final conclusion is that currently it is not possible to talk about fully autonomous weapon systems (in reference to the existing weapon systems).
En example basing on cars