Why was there a definite shift in dominance from battleships to submarines in World War 2?

Answer 1

The primary reason for the shift to Submarines rather than Battleships and other surface combatants is that in previous wars, most naval engagements were between surface warships, or warships against merchant vessels. With the advent of better submarine technology in WWI, and the early successes of the Kriegsmarine U-Boats in the Battle of the Atlantic, it became apparent that submarines as a weapons delivery platform had become a viable threat.

Advances in Air Power had shown also that Battleships were vulnerable to airplane attacks; until that time, airplanes were not believed to be capable of sinking or seriously damaging a Battleship. However, a static controlled test (the results of which were initially "skewed" by the Navy) conclusively proved that airplanes as a mobile artillery delivery system (bombers and torpedo planes) were a serious threat to the Battleship. The sinking of the Bismarck by WWI vintage torpedo planes from the British carrier Ark Royal, along with the Japanese attack at Pearl Harbor, were the final nails in the coffin of the Battleship as the premier weapons platform of the fleet. After that, carriers and submarines were the preferred weapons of choice, and remain so today because of their ability to be rapidly positioned in hot spots around the world. Carriers are more obvious since they cannot be easily hidden - they are an overt statement of a country's projection of power around the globe. However, no carrier battle group is ever without a submarine escort.

While the carrier can project air power to any part of the planet, and has today become a symbol of the host country's overall power, the submarine's inherent ability to control the shipping lanes and stop supplies are what led to Japan's ultimate defeat in WWII. Though they had carriers early in the war, they failed to replace them. As their supply lines grew longer and longer across the Pacific, it became easier for American submarines to interdict and destroy enemy shipping and cutoff vital supplies. Even today, most heavy supplies are moved by ship, as well as strategic minerals and raw materials necessary for National Security. It is this reason why the Navy exists to begin with - to control the seas and shipping lanes and ensure that vital supplies necessary to the country get here.

There are many raw materials that the US needs to survive that are not found within the borders of the US; they must be shipped in via merchant vessels. Oil is but one strategic import; Titanium is widely used in aerospace applications, but is not found here. The list of strategic materials is longer than most people realize, but it is oil that is usually singled out.

Submarines in World War II were not true submersibles as we know them today; they were surface vessels with a limited ability to remain submerged for extended periods. It wasn't until the advent of Nuclear Power in the '50's when Admiral Rickover led the effort to design, build and install the first reactor in a submarine that the true submarine was born. Today, only crew limitations require submarines to enter port and resupply.