A major difficulty in simulating Earth’s climate system is that there are interactions across scales, so that the large time and space scales can be sensitive to processes on small scales. As the computational resolution of global ocean models has improved, scientists have begun to suspect that kilometer-scale eddies and fronts, called “submesoscale” variability, have a net effect on ocean-atmosphere heat exchange that is larger than the heating from the greenhouse effect (Su et al. 2018). State-of-the-art computer models agree in predicting that these eddies have important long-term effects on the upper-ocean, but their predictions are sensitive to relatively small details in model physics and implementation. The resolution and detail of these simulations has surpassed our ability to ‘ground truth’ them with spaceborne or in situ sensors. There is thus a pressing need for a comprehensive benchmark data set on these submesoscale motions to address this important source of uncertainty in simulating the global ocean.