The Japanese Ministry of Defence is planning to increase the Maritime Self Defence Force's (MSDF) submarines to 22 units from 16.
Japan's basic defence programme for fiscal 2011 to 2015 is set to be compiled in December, amid increasing naval activity by China in waters near Japan, according to Kyodo News.
The larger submarine fleet for MSDF will improve its vigilance capacity in nearby waters, particulary the East China Sea.
The ministry also has plans to buy one new submarine each year and extend the decommissioning period of existing vessels, according to the Straits Times.
The procurement will be the largest submarine capability that Japan has maintained since its first defence programme in 1976.