The results of field tests on the response of floating ice sheets to moving loads are presented and discussed. To measure time-dependent deflections under moving loads, a convenient method that does not require reference to a fixed datum is developed. This method is based on integrating the output of a sensitive slope indicator. The data support the available theory in most respects. Deflection under a load moving at constant speed is maximized when the speed is equal to a critical value. The critical speed is essentially a function of ice thickness and water depth. Observed critical speeds for ice thicknesses and water depths in the ranges 0.3−1.4 and 1.8−54.3 m, respectively, are generally 10% higher than predicted values; these ranges include present data and earlier data by others. The data show further that critical deflection and strain can be up to 4.6 and 1.4 times the corresponding static loading values. Discussion of this finding points out that abrupt speed changes should be avoided.