The primary objectives of this contract were to design a physics package and to characterize the voltage controlled crystal oscillator (VCXO), which will satisfy the temperature and vibration requirements of a tactical rubidium frequency standard unit (FSU). The double buffer gas resonance cell has demonstrated temperature performance that exceeds the requirement. Vibration sensitivities of a FSU have been analyzed. Improved FSU design under the tactical vibration inputs are discussed in detail with performance predictions. Experimental results are shown to demonstrate validity of the predictions. The SC-cut VCXO, the state-of-the-art, provides realistic potential for use in tactical FSU. (Author)