An apparatus is provided for rapid loading and unloading of large volumes of liquid to and from a cargo transport, herein a landed aircraft transport. At a ground station, liquid is loaded from, or unloaded to, a reservoir equipped with a positionable, extendible hollow tubular boom having a cross-sectional flow area exceeding thirty square feet. At the extendible end of the boom, a valve closure is provided, movable by a power-driven ball-screw actuator between a retracted position closing the open end of the boom and an extended, open position spaced forwardly of the boom end. A cooperating valve assembly and receptacle for receiving the positionable boom end are mounted on the aircraft in a wing section, accessible by a fold-away hinged wingtip. A movable, normally closed valve closure of the aircraft valve assembly is opened by an axially movable central plunger mechanism, engagable and axially displaceable by articulated fingers on a forward face of the boom valve closure, such that the plunger is depressed inwardly of the aircraft valve assembly as the boom is moved into place. Thereupon, the boom valve closure is opened by the power screw actuator. Internally of the aircraft valve assembly, an overcenter valve-locking toggle mechanism is responsive to the displacement of the plunger, so as to unlock the aircraft valve and allow it to be driven rearwardly to an open position in unison with the opening of the boom valve closure. A peripheral, inflatable seal is provided on the rim of the seated boom end for selective sealing of the mated boom and receptacle during liquid loading and unloading. After transfer of the liquid load, the boom valve closure is retracted by the screw actuator, the aircraft valve is closed and locked by the internal toggle mechanism, the peripheral seal is deflated, and the boom is retracted. To permit loading and unloading of low-temperature liquified gas, the toggle-locking assembly for the aircraft valve is constructed to compensate for thermal expansion and contraction of the structural members to insure a stable, positive, sealed closure of the aircraft valve during flight. Extension and alignment of the sizable boom into engagement with the aircraft receptacle is achieved by controlled servomechanisms for angulating and telescoping a pair of movable, interconnected boom sections, with fine alignment and positioning of the boom being automatically effected by a position probe sensor system which develops position error signals for operating the boom servomechanisms.