  This paper presents field results and lessons learned from the deployment of
aerial robots inside ship ballast tanks. Vessel tanks including ballast tanks
and cargo holds present dark, dusty environments having simultaneously very
narrow openings and wide open spaces that create several challenges for
autonomous navigation and inspection operations. We present a system for vessel
tank inspection using an aerial robot along with its autonomy modules. We show
the results of autonomous exploration and visual inspection in 3 ships spanning
across 7 distinct types of sections of the ballast tanks. Additionally, we
comment on the lessons learned from the field and possible directions for
future work. Finally, we release a dataset consisting of the data from these
missions along with data collected with a handheld sensor stick.
