This article makes more discussions toward the paper which has been presented at the 18th International Stirling Engine Conference to improve the completeness of the statement. The presented paper addressed the requirement of the application of Stirling Engine in Submarines, reviewed relevant submarines of different countries to analyze the power required to drive submarines underwater, and pointed out the requirement of specific equipment such as heating device and heat exchanger to keep submarines navigating at proper speed when underwater navigation. It presented if the traditional basic design of Stirling engine was modified, its fuel economy should be increased. However, it does not provide any evidence to support its argument. This article collects more related researches in the world, and further verifies the above arguments especially about the power output after make more analyses and comparisons.