The strength of wet granular ice layers is an important quantity for modelling the behaviour of ice accretions encountered in aircraft engine icing since it determines the dynamics of the collision of ice crystals, their penetration into the layer, breakup and the characteristics of the ejected material. In the present study, impact tests of 3.18 mm nylon spheres are conducted on wet granular ice layers for a dynamic strength characterization. An experimental setup and methodology are designed to measure the crater depth for impact velocities ranging from 5 ms−1 to 90 ms−1. Experiments are conducted using both ice layers generated by ice crystal accretion on a solid substrate inside an icing wind tunnel and artificial ice layers prepared in a laboratory environment. By fitting the Poncelet penetration equation to the experimental data, two dimensionless parameters are derived that characterize the strength of the investigated ice layers in relation to the layer inertial resistance and apparent yield strength. A key finding is that strong connections between individual ice particles exist for ice layer generated in the wind tunnel, originating from re-freezing of liquid water near the particle contacts. Only by re-enforcing the ice particle connections in ice layers prepared in the laboratory, comparable strength values are obtained. The presented methodology enables measurement of ice layer strength and comparison at different facilities as well as conducting advanced experiments with realistic ice layers in a laboratory environment.