Well, the reason you don't hear much about Japanese submarine warfare was that they tended to use their submarines to screen their own fleets, or provide reconnaissance and striking power against the enemy fleet. In fact, the doctrine that remained (based very much on Alfred Thayer Mahan's Influence of Sea Power on History) was that when war broke out with the United States, Japanese submarines would whittle down the American fleet as it approached Japanese waters, at which point the main Japanese fleet would crush them in a decisive battle. Yamamoto and the rise of the aircraft carrier threw a giant monkey wrench into these plans, and in the end it was the Japanese strength that was whittled away, and in 1944 they lost their air power at the Battle of the Philippines Sea and the rest of their naval power at the Battle of Leyte Gulf shortly after.

That said, submarine warfare was incredibly important in the Pacific theatre - the Americans managed to succeed in strangling Japan through unrestricted submarine warfare (which was what Germany failed to do to Britain). They didn't accomplish much for the first couple of years, but that was mainly due to American torpedoes not working properly - very little credit goes to the Japanese navy, as it considered anti-submarine warfare to be beneath them, and never bothered developing it in any proper capacity. Once the torpedo problems were solved, they starved Japanese industry so successfully that by the time the USAAF was able to commence strategic bombing on Japanese factories, the factories had been shut down for weeks from lack of materials to work with.