Many mangrove replanting programs fail due to the drifting of the mangrove sapling by waves and coastal currents soon after the replanting. Hence, adequate wave protection for the mangrove planting site is required to enhance the survivability rates of the newly planted saplings. A small scaled modular submerged semicircular breakwater (SBW) is perceived to be a viable option to provide the required level of wave protection to mangroves. The study is set to investigate wave transmission, reflection, and energy loss by a SBW subjected to different immersion depths under a regular wave environment via physical modelling. The SBW model was tested in a wave flume and was subjected to relative immersion depth, i.e., a ratio of water depth to the height of the SBW, of 1.00 and 1.33, and wave steepness ranging from 0.02 to 0.06. The alternatively submerged SBW was found to be an effective breakwater design to provide the required level of wave tranquility to various coastal applications. © 2024 EDP Sciences. All rights reserved.