External vibration testing was performed on a semi-hermetic, direct drive compressor on magnetic bearings intended for U.S. Navy Shipboard use. The compressor was placed on a U.S. Navy MIL-STD-167 shaker platform and driven at sinusoidal frequencies from 4 to 33 Hz at graduated displacements equal to a maximum of 1.5Gs. During the machine design phase, a linear forced response analysis of the coupled rotordynamic system model of the rotor, housing and magnetic bearings was performed to predict rotor/housing displacements and actuator loads. The results were used to guide bearing sizing and control algorithm design. The measured rotor motion and actuator currents correlated well with predictions at all tested frequencies, amplitudes and orientations. Analysis methodology, test results, and comparisons are reported here.