The papers in this special section focus on sensor system deployment in the field of oceanography. Oceans regulate the Earth's climate and are integral to all known sources of life. Ocean processes are of biological, geological, chemical, or physical nature, occurring at micro- to kilometer scales, from less than seconds to centuries, turning the understanding and the sustainable management of the ocean into a multiscale and multidisciplinary effort. Collection of in situ observation of a volume that covers over 70% of the planet is also inherently challenging and remains generally difficult and costly in time and resources, with so far a rather unsatisfactory result, in particular with respect to space-time resolution. Over the past decade, there has been a steady crescendo of interest to support the development of a truly integrated and sustainably funded Ocean Observing System. This will be achieved with more long-term measurements of key parameters but is impaired by the costs and lack of reliability of ocean sensors in general.