Measurements were made on the propulsion system of the USS SIMON LAKE (AS-33) in February 1965 as part of a program to improve analysis procedures used by the Navy for predicting the longitudinal vibration of shaft propulsion systems. The objectives were to find the axial exciting forces and damping associated with the propulsion system of this ship, as well as to determine how the gear case, turbines, condenser, and machinery foundation affect longitudinal vibration. Alternating thrust in the shaft and longitudinal displacement of the gear case, low-pressure turbine, condenser, and machinery foundation were measured. A resonance was found to exist in the operating range, but it is not considered detrimental. The gear case, turbines, and condenser move essentially as one unit. A mass-elastic system derived from measured data includes a level effect acting on the foundation mass. The exciting forces are lower than usual, except at or near full power.