Abstract
Prior to the seminal work of Chuprov and Grachev, who introduced the underwater acoustic waveguide invariant, the asymptotic equivalent of the same quantity was recognized as playing an important role in Hamiltonian dynamics. A consequence is that the waveguide invariant controls, to a large extent, underwater acoustic ray dynamics. In this presentation some of the less well known properties of underwater acoustic wavefields, based on both ray- and mode-based descriptors, that are controlled by the waveguide invariant are reviewed. These properties include overall wavefield structure, ray stability, time spreads and modal dispersion. [Work supported by ONR.]