An important milestone in the development of ESA’s tenth Earth Explorer satellite mission, Harmony, has been reached thanks to two aircraft flying in tight formation over the Dutch Wadden Islands collecting key data on sea state and currents. The main purpose of this tricky airborne experiment is to mimic the geometry at which the Harmony satellites will measure various aspects of ocean dynamics to understand how air and the ocean surface interact, which, in turn, will improve weather prediction and climate models.