This paper provides the result of the empirical study on enhancing the accuracy of software cost estimation model for defense software development project applications. It is very important to build a software cost model adequate to the environment for the accurate results of the estimation. Calibration can be used for building its own software cost model by using preexisting model such as the COCOMO II. In this paper, we practiced the calibration of the COCOMO II model using data collected from the defense software development projects by using calico calibration software. The results show that the estimation accuracy became enhanced after calibration. Also we found that the performance of calibrating both the multipliers and exponent is better than calibrating multipliers only. Finally this paper includes comments on reasons of the lower calibration performance and future works to enhance the estimation accuracy.