Japanese Maj. Gen. Jiro Hiroe turned to numbers to explain why Japan is taking part in U.S.-led exercises to develop skills in moving troops from sea to shore: his nation has 6,852 islands and 6,414 of them are uninhabited.

"Therefore developing amphibious capabilities is an urgent challenge for Japan," Hiroe, of the Japanese military's policy and programs department, said Wednesday.

Other countries in the Asia-Pacific region are similarly interested in developing vital-yet-difficult-to-master amphibious skills, either to provide aid after tsunami or other disasters or to defend islands claimed by neighboring states.

In a sign of that, officers from 23 nations gathered in Hawaii this week for a three-day symposium hosted by the U.S. Marine Corps. Many leaders also attended a panel discussion on amphibious capabilities at an Army meeting on land power in the Pacific in Waikiki.

Japan didn't have the amphibious capabilities in 2011 when a magnitude-9 earthquake struck and sent tsunami slamming into its northern coastline, Hiroe said. Japan turned to the U.S., which sent the Okinawa-based 3rd Marine Expeditionary Force to help with relief efforts.

Japan has since started to form its own amphibious forces. In addition to disaster relief, amphibious skills could help it defend small islands in the East China Sea that it controls but that China claims as its own.

Malaysia, the Philippines and Vietnam, who each have territorial disputes with China in the South China Sea, also joined the amphibious symposium.

The meeting featured presentations from each of the participating nations and discussions of how they could work together. Participants got to observe an amphibious landing in person on Tuesday when U.S. Marines and sailors demonstrated storming a beach at Bellows Air Force Station on Oahu.

Marine Lt. Gen. David Berger, the commander of the 1st Marine Expeditionary Force at Camp Pendleton, said most nations at the gathering were looking to speed up their acquisition of amphibious skills.

"The countries — most of them — are in the beginning stages of developing the capability but they don't want to take 50 years to develop it. So the best way to do that is to go learn from someone else," he said.