Tarawa did turn out to be a "productive proving ground" for the amphibious doctrine. In fact every subsequent move in the drive across the central pacific was to be made with the mistakes of Tarawa in mind. The lessons learned and adjustments made to the doctrine helped take the Marshalls twice as fast with half the casualties. The practical lessons of amphibious warfare [at Tarawa] provided for adjustments and improvements in all six parts of the doctrine. But what must be recognized and remembered about Tarawa was that it was the individual marine, his courage, bravery and training which bought the victory and time for adjustment which sold the doctrine.
The doctrine may have been sound, and the correct method to seize an enemy base, island or hostile shore, but it was in disarray and failing on Tarawa. It took the Marines to catch and save it from failure; Marines who relied on traditional bedrock foundations of the Corps. Edwin Hoyt put it best, "without the heroism of the Marines at Tarawa, the entire course of the Central Pacific might have changed." Tarawa should not stand as the proof of amphibious doctrine, but as the symbol of raw courage and Marine tradition.
Additional Sources: www.mcu.usmc.mil
www.history.navy.mil
www.ibiblio.org