A dry dock is exactly what it sounds like: a dock for ships, submarines and any aquatic vehicle, which is emptied of water. It’s used to repair and build with easy access to the hull and underside, while the vessel is suspended off the bottom.
The dry dock gates then close and the water is pumped out, leaving the boat supported by a series of blocks. Once work has been completed the dock floods again, the gates open and the renovated vessel floats out.
Floating dry docks can take the place of the terrestrial variety where space on the land is limited or portable ship repair is required by the same company in remoter regions.