A user actuated liquid drug transfer device for use in a Ready-To-Use liquid drug transfer assemblage for establishing flow communication between a liquid source and an injection vial, the injection vial including a closed end vial tube, and a tubular vial crown having a crown opening stopped by an injection vial stopper, the injection vial having an uppermost injection vial surface, the liquid drug transfer device having a longitudinal device centerline and comprising: (a) an injection vial adapter having a transverse injection vial adapter top surface and a downward depending injection vial adapter skirt intended for telescopic mounting on the vial crown, said transverse injection vial adapter top surface including a transverse injection vial adapter top surface aperture along the longitudinal device centerline overlying the uppermost injection vial surface on said telescopic mounting on the injection vial; (b) a liquid source adapter intended for attachment to the liquid source, said liquid source adapter including a transverse liquid source adapter top surface and a downward depending liquid source adapter skirt mounted on said injection vial adapter in a pre-actuated state of the liquid drug transfer device and configured for telescopically receiving said injection vial adapter therein in an actuated state of the liquid drug transfer device on user compaction of the liquid drug transfer device from said pre-actuated state to an actuated state; (c) a dual ended liquid transfer member having an upward liquid transfer member end for flow communication with the liquid source and a downward liquid transfer member end in flow communication with said upward liquid transfer member end and terminating in a puncturing tip for puncturing the injection vial stopper for flow communication with the vial tube, said puncturing tip being configured to overlie the uppermost injection vial surface in said pre-actuated state and to puncture through the injection vial stopper in said actuated state; and (d) a snap fit securing arrangement for securing said liquid source adapter on said injection vial adapter in said actuated state; characterised in that the liquid drug transfer device further comprises: (e) a safety catch mechanism requiring an initial manual linear sliding extension for extending said liquid source adapter from said injection vial adapter for priming the liquid drug transfer device to an intermediate primed state, thereby enabling said user compaction from said pre-actuated state to said actuated state; and (f) an extension limit arrangement for limiting said linear sliding extension of said liquid source adapter from said injection vial adapter in said intermediate primed state. (a) an injection vial adapter having a transverse injection vial adapter top surface and a downward depending injection vial adapter skirt intended for telescopic mounting on the vial crown, said transverse injection vial adapter top surface including a transverse injection vial adapter top surface aperture along the longitudinal device centerline overlying the uppermost injection vial surface on said telescopic mounting on the injection vial; (b) a liquid source adapter intended for attachment to the liquid source, said liquid source adapter including a transverse liquid source adapter top surface and a downward depending liquid source adapter skirt mounted on said injection vial adapter in a pre-actuated state of the liquid drug transfer device and configured for telescopically receiving said injection vial adapter therein in an actuated state of the liquid drug transfer device on user compaction of the liquid drug transfer device from said pre-actuated state to an actuated state; (c) a dual ended liquid transfer member having an upward liquid transfer member end for flow communication with the liquid source and a downward liquid transfer member end in flow communication with said upward liquid transfer member end and terminating in a puncturing tip for puncturing the injection vial stopper for flow communication with the vial tube, said puncturing tip being configured to overlie the uppermost injection vial surface in said pre-actuated state and to puncture through the injection vial stopper in said actuated state; and (d) a snap fit securing arrangement for securing said liquid source adapter on said injection vial adapter in said actuated state; (e) a safety catch mechanism requiring an initial manual linear sliding extension for extending said liquid source adapter from said injection vial adapter for priming the liquid drug transfer device to an intermediate primed state, thereby enabling said user compaction from said pre-actuated state to said actuated state; and (f) an extension limit arrangement for limiting said linear sliding extension of said liquid source adapter from said injection vial adapter in said intermediate primed state.