The ability of microwaves to penetrate dielectric materials has been shown to produce unique inspection capabilities and potentially large cost benefits when applied to some inspection tasks usually performed using more traditional NDE methods. Fibre reinforced polymeric (FRP) materials and in particular FRP sandwich composites are finding increased use in the field of maritime structures and this investigation has demonstrated the ability of microwave NDE to detect near-side, core and far-side defects including skin / core debonding, core cracking and impact damage. It is also the case that maritime vessels employ large volumes of lagging materials to restrict heat emission from pipework and also to prevent condensation, e.g. on the inner side of a hull. Defects may grow unseen beneath this lagging and it is traditionally only by removal of all insulation that an NDE inspection may be performed. However, by employing the ability of microwaves to pass through non-conducting media it has been shown that not only defects within FRP structures, but also, corrosion /wall thinning and surface breaking defects in metallic components can be detected without the necessity of removing lagging. It is therefore envisaged that such an inspection method would lead to large cost benefits to the owners and operators of such vessels. Monolithic composite structures are readily inspected by this method. It has been shown that core defects in sandwich composite structures can successfully be detected. The fact that microwaves are susceptible to the surface finish of conductors enables microwave NDE to be used to inspect a metallic surface for cracks and corrosion without the need to remove lagging. It is now intended that prototype production systems are produced to enable a greater depth of in service inspection experience to be gained. Future investigations will include an assessment of pulsed techniques to enable time domain, i.e. defect depth, information to be obtained.