In Table 2, a large operation period means that there are many naval operations. That is, the degree of exposure to failure is large. The coefficient of both variables is 0.58. At this time, since many failures occur, the cost of spare parts will be larger during the total lifecycle. This is interpreted intuitively. However, the coefficient of operation period and cost of spare parts during the total lifecycle is -0.86. This can be found in the Navy’s maintenance policy. In the current policy of 1.5 months maintenance after 4.5 months of operation, if the operation period is increased, the total number of preventive maintenances performed during the total lifecycle decreases. In other words, it is also interpreted to mean that the cost of spare parts used for preventive maintenance is higher than the cost of spare parts caused by critical failure during the total lifecycle. Even if the unit price of spare parts used for critical failure is much higher than the cost used for preventive maintenance. This may seem simple to interpret, but to naval policy makers, it is not. This is because the increase in total lifecycle cost caused by the increase in critical failure was taken for granted. When the correlation of all variables is checked, the more complex the relationship, the more difficult it is to interpret. However, the analysis results can be used as important. Among them, the interpretation that maintaining the current policy could lead to catastrophic results was also found. If the DT model is used, potential problems caused by the latent effect can be discovered only by correlation analysis.