A retractable U-shaped ladder assembly preferably for a craft such as a watercraft has a rotatably retracted ladder which is attached to the craft by brackets. A torsion spring is used to bias the ladder into the retracted position. While the ladder is in an in-use position, the ladder is locked into place by a locking mechanism. The locking mechanism includes a bent plate which presses against four rings that are fixed to a rod, which rod extends from each bracket. Each ring has a notch that is located in the same position. In the use position, the bent plate will fit into the notches of the rings and lock the step. When the user is finished using the ladder, the user can manually unlock the step by pressing the bent plate. The bent plate moves out of engagement with the notches in the rings, thereby allowing the torsion springs in the brackets to rotate the step to the retracted position.