A repairable system is one which can be restored to satisfactory operation by any action, including parts replacements or changes to adjustable settings. This paper presents the field data analysis of a repairable system. Field data is collected for a weapon system performing functions such as command, armed control, target search, acquisition and tracking, etc. The MIL-HDBK-189 test and Laplace test are performed to confirm the trend of the time between failures(TBFs), and it is found that no trend exists. Thus, the maximum likelihood and least square estimates of MTBF(mean time between failures) of the system is estimated for the exponential distribution suitable for the TBFs.