The Navy uses many devices whose operation depends on the hydrostatic principle. Hydrostatic pressure refers to pressure at any depth in a liquid that is not flowing. Pressure depends upon both depth and density. The working principle of all hydraulic mechanisms is simple enough. Machines that operate liquids under pressure are called hydraulic machines.
Liquids are incompressible.
They cannot be squeezed into spaces smaller than they originally occupied. A force applied on any area of a confined liquid transmits equally to every part of that liquid. In hydraulic cylinders, the relation between the force exerted by the large piston to the force applied on the smaller piston is the same as the relationship between the area of the larger piston and the area of the smaller piston. Tubing requires little space. Few moving parts are required.