Repair Tasks
Underwater repairs are usually minor. They are done on the submerged parts of a ship (the propeller), the rudder of the ship, the cathodic protection system, etc.), on oil platforms and other pieces of machinery. Only special teams or groups of experienced divers can do such tasks because there is certain knowledge that must be acquired for the accomplishment of the repair. Usually, the task starts with an inspection of the working spot, selection of methods and instruments, planning the operation, the doing of the task and checking whether everything is on order.

Such repairs are often done in ports (not in open sea). There are some demandings for the safety of divers: the propeller should be locked, the ship should be stable and no objects should be thrown over board when there is a diver under water. Sometimes, it is also recommended to have a means of attachment to the side of the ship - a line or magnets. 

Below you see pictures of divers repairing the hull of a ship. The Earth emits magnetic field which damages the hull of the moving ship. That is why, divers apply protectors made of brass to it. When the alloy is worn over, divers coat the hull with new protectors.
 
 

Salvages
The salvage of a sunken ship, plane, submarine, cargo, etc. from the sea bottom is performed in several ways. The choice of technique is conformable to the weight and volume of the item. There are four main ways of salvaging - using the line to tie the object and lift it, attaching a flotation device to it, restoring the flotation of the sunken object. If it is small and light, the diver can carry it to the surface. Sometimes, if the object is buried in silt, the silt is cleared with the help of a water jet or an air hose. When salvaging an item, the diver should be very careful not to swim under it because in case of accident, the object might start to sink and hurt the diver.

Others
Other industrial procedures include building bridges, ports, oil platforms, underwater mining, repairing flooded underground facilities (subway).