Nacelle for a bypass turbojet, said nacelle comprising: - a fixed structure comprising a fixed cowling, - a movable cowling movable in translation relative to the fixed cowling in a translational direction parallel to a longitudinal axis X between a closed position, in which it is near to the fixed cowling, and an open position, in which it is remote from the fixed cowling, towards the rear, such as to define between them an opening between a duct for a secondary flow and the exterior of the nacelle, - drive means designed to move the movable cowling from the closed position to an intermediate position, then to the open position, and vice versa, - a blocking door mounted to be movable in rotation about a rotation axis on the movable cowling between a stowed position, in which it is positioned outside the duct, and a deployed position, in which it lies across the duct, and - a deployment system (150, 650) provided such as to coordinate and to delay the passage from the stowed position to the deployed position of the blocking door relative to the passage from the closed position to the open position of the movable cowling, and vice versa, said deployment system (150, 650) comprising: - an arm comprising a first end mounted in an articulated manner on the blocking door and a second end that bears a stop, - a slider that is fixed to the arm, - a linear guide system that is fixed on the fixed structure and guides the slider parallel to the translational direction, and - a cam (158, 658), where the stop is arranged such as to lie against the cam (158, 658) when the movable cowling reaches the intermediate position from the closed position and such as to be guided by said cam (158, 658) in such a manner as to drive the rotation of the arm about the slider about an axis of deployment parallel to the axis of rotation when the movable cowling moves from the intermediate position to the open position. - a fixed structure comprising a fixed cowling, - a movable cowling movable in translation relative to the fixed cowling in a translational direction parallel to a longitudinal axis X between a closed position, in which it is near to the fixed cowling, and an open position, in which it is remote from the fixed cowling, towards the rear, such as to define between them an opening between a duct for a secondary flow and the exterior of the nacelle, - drive means designed to move the movable cowling from the closed position to an intermediate position, then to the open position, and vice versa, - a blocking door mounted to be movable in rotation about a rotation axis on the movable cowling between a stowed position, in which it is positioned outside the duct, and a deployed position, in which it lies across the duct, and - a deployment system (150, 650) provided such as to coordinate and to delay the passage from the stowed position to the deployed position of the blocking door relative to the passage from the closed position to the open position of the movable cowling, and vice versa, said deployment system (150, 650) comprising: - an arm comprising a first end mounted in an articulated manner on the blocking door and a second end that bears a stop, - a slider that is fixed to the arm, - a linear guide system that is fixed on the fixed structure and guides the slider parallel to the translational direction, and - a cam (158, 658), where the stop is arranged such as to lie against the cam (158, 658) when the movable cowling reaches the intermediate position from the closed position and such as to be guided by said cam (158, 658) in such a manner as to drive the rotation of the arm about the slider about an axis of deployment parallel to the axis of rotation when the movable cowling moves from the intermediate position to the open position.