The breakwater consists of a floating slab of breadth comparable to the length of the wave to be obstructed. Performance is improved by various arrangements of slots and mass-damping. The breakwater acts primarily by inhibiting the vertical component of orbital motion; there is a secondary action of energy dissipation by wave-breaking and eddy-making; there is also a degree of reilection. Mooring forces are small; it seems that on an exposed ocean coast, forces of the order of 0.5T per ft. lin. should be catered for. The following series of tests have been carried out; the basic measurements being of wave reduction and mooring force; typical results are shown in diagrams. 1) On models of lengths 3*-4' in the Southampton University tank using wind generated waves. 2) Do. Do. Using .paddle generated waves of lengths up to 8'. Series (l) and (2) comprised observations on some forty different configurations. 3) In the National Physical Laboratory tank using a model hZ' x 30' overall and waves of lengths up to 35'- Bending strains and vertical displacements were measured. k) A model has been installed in Queen Mary Reservoir, Staines of 100' x k7' overall; gale force winds are awaited which are expected to produce waves of the order of ko' 1. 5) A 1/100 scale model has been installed in a harbour model at the Franzius Institute, Hanover, where the effect of the breakwater in a scaled-down natural site has been investigated. 6) Tests in development of (l) and (2) above are being carried out at the laboratories of Messrs. Taylor Woodrow Ltd. at Southall, London.