Abstract: A linear preload fluid power operated latch has two coaxial pistons, one slidable inside the other and the other slidable within a cylinder. The one piston slides inside the other to cam dogs which are slidable in slots of a nose which is secured to the other piston so as to engage an undercut in a cup in which the nose is received. After the dogs are engaged in the cup, which secures the latch, both pistons are retracted to apply a linear preload force between the two bodies being latched. In one embodiment, the pistons are moved in both directions under fluid pressure and in another embodiment, both pistons are returned by compression springs. In either case, the cup is drawn closer to the cylinder with a certain preload force, to latch a body to which the cup is attached to a second body to which the cylinder is attached with that preload force.