A common technique to increase the thermal efficiency and the power output of gas turbines is to inject water upstream of the compressor section. Through the evaporation of the water throughout the compressor, an isothermal process is approached. A recently developed technology for this enhanced process is interstage injection in which water is injected directly between the stages. One advantage of this over wet compression is the avoidance of icing, since the local temperatures at the injection positions are already above melting point. Moreover, stage characteristics and load distribution can be rearranged within the compressor by individually adjusting the injection amount in different stages. However, there is little practical understanding of this process, and suitable injection methods have still to be found. This paper therefore demonstrates the implementation of a novel technology of interstage injection in an axial compressor test rig whereby twin jet nozzles are integrated directly into the trailing edge of the first stator row to deliver a homogenous spray over the entire radial span. Due to the resultant blade complexity, blades are manufactured by selective laser melting (SLM) and subsequently installed in an enhanced four-stage axial compressor. The installed control and measurement principles of the test rig are presented and results demonstrate the functionality of the innovative design.