Sound: wave motion, sound pressure etc. Arrays: Need for projector arrays, Need for hydrophone arrays etc. Propagation of Sound in the Sea : Propagation loss, Losses: Spreading losses, Absorption losses. Target Strength: Definition, Formulae, Measurement, Dependence on pulse type and duration. Noise in Sonar Systems: Sources of nose, Thermal noise, Noise from the sea, Noise from a vessel. Reverberation: Sources of reverberation, Scattering and reflection; The Sonar Equations: What are they? What are their uses? The basic sonar equation, The basic passive equation; Passive Sonar: Radiated noise, Radiated noise: source level, nature of radiated noise. Active sonar: Pulse types, CW processing, FM processing, Active sonar equations.