Abstract:  Mapping of the ocean floor has been identified as an international grand challenge because no existing technology offers both high-resolution and fast coverage rate. Meter-scale resolution seafloor maps, necessary for applications such as search and resource exploration, are obtained by sending sensors deep into the ocean – a slow and difficult approach to mapping large areas. Low-frequency sonar can propagate across the long distances underwater potentially providing fast coverage, but diffraction and ship size constraints limit the attainable resolution.  A novel future mapping capability could deploy a small fleet of USVs to create a sparse array ten to a hundred times larger than existing, fixed hull-mounted arrays. The larger effective array produces a narrower beam enabling higher resolution maps at deeper depths. To demonstrate that this is feasible, our team conducted a series of risk reduction efforts culminating in the deployment of a rigid sparse aperture sonar array (8 m × 8 m) in Cape Cod Bay.