Design Development Report was prepared for the Mechanical, Electrical, Plumbing and Smoke Detection system of the two Service Tunnels. The Design Development was based on the Schematic Design developed from the tender submission and as per the further progress towards final working drawings. The project involves construction of Two 750 Meters long Sub Sea Tunnels consisting of 132 kV cable support system. Seepage Pumping System, Ventilation System, Lighting and utility power system. System engineering was done for Primary and Secondary Pumping arrangement to remove seepage water. Ventilation system was designed to maintain temperature within the tunnel of 132 kV and acceptable level of Indoor Environmental quality with the help of smoke detectors and purging system to remove any smoke and provision for smoke ventilation fan at one end of the tunnel. Smoke detection system was designed to identify and annunciate smoke condition within the tunnel. Providing even distribution of conditioned air through package AC at both ends of the tunnel was ensured. System engineering for Lighting System was done to illuminate the tunnel and illuminate under power failure/emergency situation. Provisions for small power were made.