A ducted fan gas turbine assembly having: a propulsive fan driven by a core engine, an annular bypass duct which receives an airflow from the fan and is bounded on the radially inward side by the core engine and on the radially outward side by an engine nacelle, the bypass duct terminating in a primary discharge nozzle for the duct airflow, and a thrust reverser assembly having a vane arrangement including a first set of turning vanes for channelling airflow from the duct in a rearward direction, and a second set of turning vanes for channelling airflow from the bypass duct in a forward direction; wherein the nacelle has a stationary cowl portion and a movable cowl portion which is translatable rearwardly relative to the stationary cowl portion to open an annular gap therebetween, the cowl portions (32, 33) cooperating with the thrust reverser assembly to provide first, second and third operational configurations, whereby in the first operational configuration the gap between the cowl portions (32, 33) is closed and the vane arrangement is stowed in the nacelle to prevent airflow from the duct flowing therethrough, in the second operational configuration the first set of turning vanes is positioned in the gap opened between the cowl portions (32, 33) to form an annular secondary discharge nozzle from the bypass duct for the duct airflow, such that the total effective flow area of the primary discharge nozzle and the gap in the second operational configuration is greater than the total effective flow area of the primary discharge nozzle in the first operational configuration, and in the third operational configuration the second set of turning vanes is positioned in the gap opened between the cowl portions to divert the duct airflow through the second set of turning vanes and provide reverse thrust, characterised in that the vane arrangement is translatable rearwardly from a forward position in the first and second operational configurations to a rearward position in the third operational configuration. a propulsive fan driven by a core engine, an annular bypass duct which receives an airflow from the fan and is bounded on the radially inward side by the core engine and on the radially outward side by an engine nacelle, the bypass duct terminating in a primary discharge nozzle for the duct airflow, and a thrust reverser assembly having a vane arrangement including a first set of turning vanes for channelling airflow from the duct in a rearward direction, and a second set of turning vanes for channelling airflow from the bypass duct in a forward direction; wherein the nacelle has a stationary cowl portion and a movable cowl portion which is translatable rearwardly relative to the stationary cowl portion to open an annular gap therebetween, the cowl portions (32, 33) cooperating with the thrust reverser assembly to provide first, second and third operational configurations, whereby in the first operational configuration the gap between the cowl portions (32, 33) is closed and the vane arrangement is stowed in the nacelle to prevent airflow from the duct flowing therethrough, in the second operational configuration the first set of turning vanes is positioned in the gap opened between the cowl portions (32, 33) to form an annular secondary discharge nozzle from the bypass duct for the duct airflow, such that the total effective flow area of the primary discharge nozzle and the gap in the second operational configuration is greater than the total effective flow area of the primary discharge nozzle in the first operational configuration, and in the third operational configuration the second set of turning vanes is positioned in the gap opened between the cowl portions to divert the duct airflow through the second set of turning vanes and provide reverse thrust, characterised in that the vane arrangement is translatable rearwardly from a forward position in the first and second operational configurations to a rearward position in the third operational configuration.