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Limitations in the intrinsic mechanical characteristics of a pure hydroxyapatite (HA) coating layer render it ill-suited for numerous orthopaedic implants designed to bear heavy loads. In this research, a coating composed of poly ε-caprolactone (PCL) and HA was developed and applied to stainless steel 316L using dip-coating techniques. To enhance the surface, ultrasonic processing was utilised at various temperatures. Various PCL/HA mixtures were prepared for application onto the stainless steel 316L substrate. In order to optimise the PCL/HA composite coating for enhanced bond strength and corrosion resistance, an empirical model was created using the Response Surface Methodology (RSM). A comprehensive analysis of the coated samples was conducted using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared Spectroscopy (FTIR) were employed. Furthermore, experiments involving potentiodynamic polarisation and Electrochemical Impedance Spectroscopy (EIS) were conducted within a simulated body fluid (SBF) solution. The models derived from the RSM were compared with the experimental results, revealing the close agreement between them. These models underscore the significance of the quantity of the PCL as a more critical factor than the ultrasonic temperature in improving the bond strength and corrosion resistance of the coated substrates. An optimal PCL/HA composite coating layer, with favourable mechanical and electrochemical properties, was achieved with an ultrasonic temperature of approximately 54.7 °C and a PCL/HA ratio of about 39.97% (wt.) following a drying process lasting approximately 10.68 hours.