A representation of a fundamental solution group for a class of wave equations is constructed by exploiting connections between stationary action and optimal control. By using a Yosida approximation of the associated generator, an approximation of the group of interest is represented for sufficiently short time horizons via an idempotent convolution kernel that describes all possible solutions of a corresponding short time horizon optimal control problem. It is shown that this representation of the approximate group can be extended to arbitrary longer horizons via a concatenation of such short horizon optimal control problems, provided that the associated initial and terminal conditions employed in concatenating trajectories are determined via a stationarity rather than an optimality based condition. The long horizon approximate group obtained is shown to converge strongly to the exact group of interest, under reasonable conditions. The construction is illustrated by its application to the solution of a two point boundary value problem.Keywords. Optimal control, stationary action, dynamic programming, wave equations, fundamental solution groups. two point boundary value problems. MSC2010: 35L05, 49J20, 49L20.any trajectory of an energy conserving system renders the corresponding action functional stationary in the calculus of variation sense.Consequently, Hamilton's action principle can be interpreted as providing a characterisation of all solutions of an energy conserving or lossless system. This interpretation motivates the development summarised in this work, with Hamilton's action principle applied via an optimal control representation to construct the fundamental solution group corresponding to a lossless wave equation. The specific wave equation of interest is given byẍ