Expansion of offshore oil & gas fields is inevitable. This will require significant investment in new pipelines to bring the resource onshore. 10,000km of pipelines form part of the oil & gas infrastructure in the North Sea. Combined with the huge growth in the installation of offshore wind farms & telecommunication networks, many thousands of kilometres of newly installed subsea cables & pipelines (CPs) will be required. It is critical that such underwater infrastructure is properly managed over its lifetime to ensure proper laying, inspection, quality maintenance, quick repair and comprehensive decommissioning.Existing state-of-the-art cannot currently provide a complete lifecycle solution. The SonaTag project will develop a novel low-cost position, location & identification passive underwater tag and a custom designed sonar system designed to ‘see’ the tags. SonaTag will offer CP laying contractors a means to greatly reduce the cost of CP laying operations, thereby ensuring its initial adoption in the market. Downstream stakeholders such as IMR (Inspection Maintenance and Repair) crews and governments will have the means to locate and uniquely identify these vital assets.The system will provide a robust environmentally sound solution for longterm lifecycle tagging by achieving the following objectives: specialised sonar with transmit power adequate for deployment (220 dB) at transmit end to achieve operational accuracy of +/- 0.1m @ 10m to 1000m range; the ability to detect range & position of tag in 5secs @ 1000m and 2 secs @ 10m from sonar transceiver; inert tag device with detectability in high noise environments i.e. seabed.Using this solution the project expects to comprehensively address the problem of unmanaged critical underwater infrastructure & address the high operation costs of laying CPs. In doing so, we will deliver €45 million in revenue with a profit of €9.3 million to the SME partners after 5 years, while creating over 100 high skill jobs.