Newcastle University have been advancing the field of underwater acoustic communication and positioning for over 25 years and the most recent developments are focused on ultra-low cost, low energy devices to enable the cost effective deployment of long term, large scale underwater wireless sensor networks. Results from the EPSRC funded programme USMART will be described, demonstrating that reliable communication and positioning can be achieved, over distances up to 2km, using an acoustic modem device that can be manufactured for around £50 in large quantities. Novel work on methods to minimise the environmental impact of acoustic transmissions is also discussed. The research programme to develop smart underwater sensing networks from these technologies will be described along with projects focusing on exemplar applications including cost effective marine mammal surveys, micro-AUV swarming and tagging/location of fishing gear to mitigate marine litter issues.