The Japanese Navy Underground Headquarters (JNU) was the headquarters command post for Rear Admiral Minaru Ota of the Japanese Navy. Initially, Ota had a 10,000-man strong naval force on Okinawa, most of which were supply personnel and maintenance technicians. Of the 10,000 forces on Okinawa, about 250 were trained in ground warfare, and most of that 250 was an 81mm mortar platoon. Additionally, about 1,500 of the 10,000 forces were Okinawan conscripts. Note that these forces were not part of the Japanese Navy's Naval Landing Force, which was the well-trained and efficient ground fighting arm of the Imperial Navy. The only presence of the Naval Landing Force was Rear Admiral Ota.

Ota had a distinguished career, and prior to his assignment to Okinawa, had held several Naval Landing Force commands during his career. He had been present in Nanking prior to the Rape of Nanking, but when the Rape began, he pulled his forces out, saying that they were better than the atrocities being committed, and that he wanted no part of the actions. This made him one of the few offers present in Nanking that had nothing to do with the war crimes committed there.

Transferring Ota to Okinawa was smart move on the part of the Imperial Navy commanders. In his prior service, Ota had also been a gun school instructor, and when he came to the island, he brought a staff culled from Naval Landing Forces commands. Thus, he was well placed to employ a land-based force.

The Japanese Navy Underground Headquarters was dug into a hillside on the southern portion of the island. It took 1,000 people four months to dig. Photos in the JNU museum show naval base forces digging it, but in actuality, Okinawan civilians did most of the labor. In fact, Ota was one of the few Japanese officers to save positive things about the Okinawans. He asked mainland Japan for future consideration of the Okinawan people in light of all the hardships they endured during the Battle of Okinawa.

Prior to the attack on the JNU, approximately half of Ota's forces were used in the counterassault at Hacksaw Ridge, and the remaining 5,000 were ordered around May 22 to pull down to Cape Kyan around May 22. The problem was that the orders said to fall back on May 28, and Ota misread them and fell back on the 26th. Many of the group's supplies and equipment were destroyed, and when they reached the southern portion of the island, they found nothing good to defend. So, Ota recruited a corps of 2,000 volunteers and returned to the Naval Underground. On their way, they picked up about 500 stragglers from the Japanese Army.

The group faced many problems when they returned to the Headquarters. Firstly, they lacked weapons. Many of the men didn't have rifles, so the rifle-bayonet combinations were split between men. Some men were armed with little more than bayonets tied to sticks or rudimentary spears, while others had rifles or shore guns and aircraft cannons adapted for ground fighting. These were the weapons with which they defended the Headquarters against the Sixth Marine Division.

Because Army tactics would not favor an amphibious assault, Ota expected the American forces to invade from the east. To back up his assertion, he had reports of the First Marine Divisions moving in to the south. Their objective was to cut off the peninsula and isolate it from the rest of Okinawa Honto.

The Sixth Marine Division came ashore in the area of present-day Naha Airport. But the problem was that the amtracks floundered in the port. After being constant used to run supplies, they broke down. Nevertheless, the 4th Regiment led the way to the JNU and was backed up by the 29th. Working to the south and west, they anticipated taking the objective by June 7. (This would be the final objective for the 10th Army.) Ota shifted his defenses to meet the attack. On June 9, the 27th Marine Regiment came toward the JNU from the west, making the attack two-pronged. Ota was outflanked and had only 2,500 men.

Of the forces at the JNU, 158 were captured, marking the first large group of prisoners apprehended during the Battle of Okinawa. Some awoke in the hospital and tried to commit suicide, with some attempting to bite off or chew off their own tongues. Roughly 80 of these forces survived and left the peninsula.

Many accounts say that the first American to enter the Japanese Naval Underground was a Marine colonel. Others say that the first man in was PFC Tom McKinney. On duty to find the JNU, McKinney was sitting on the side of the hill with rank charts when he saw a bush move. He pulled the bush out of the ground and found an airshaft. Through a wooden pipe, with a rope around his waist and a flashlight in hand, he descended headfirst into the tunnel. Accounts of McKinney volunteering for this duty are inaccurate. "Volunteer, hell, I didn't volunteer. I was voluntold," McKinney recounted to Chris Majewski upon returning to Okinawa in the 1990s. At the bottom of the tunnel and to the right was a passageway with a blanket over it. As McKinney began to search, a second Marine came down feet first. More than 160 men were found in the cave, and American forces estimated that they had been dead for about three days. McKinney and his fellow Marines searched cave, contacted their company, and contacted Intel, which took about two days to arrive on the scene and showed up in clean jeeps and with clean Thompson submachine guns. Upon further exploration, the Americans found Ota and his staff, but no paperwork. Intel blew the whole cave shut from the outside.

The cave system was opened as a museum in 1970. Critics counter that the site was poorly excavated and that the museum doesn't tell an accurate story. When the caves were opened, only about 70 percent of the caves were excavated, and crews didn't research what they were removing. They were simply excavating.

Additionally, the Medical Room is mislabeled. McKinney described the Medical Room as having a 55-gallon drum to the right, with tables knocked over and bottles littering the floor. Those items are still there, but are under three feet of dirt. Furthermore, the inappropriately "Medical Room" is too small for any beds. Critics assert that museum officials labeled the room as the Medical Room because wounded were found there. The real Medical Room is near the back of the JNU. The drum McKinney described is still there.

Perhaps the most controversial of displays is the room in which visitors can see blast marks on the wall. Some contend that these "blast marks" (supposedly from a member of the Imperial forces at the JNU committing seppuku with a grenade) are fake, as they don't match the blast pattern of a Japanese grenade, and there are too many dead spaces (especially above) where there are no marks. Many of the troop counts given on museum displays are inaccurate as well.

Many of the JNU's artifacts are still in the caves. About 65-70 percent of the tunnels have been excavated. The floors in the portion visitors see have been converted to concrete, and the walls have been re-surfaced. Some assert that the hallow room next to the room with blast marks might contain the missing intelligence records that American forces never found before blowing the caves closed.

Despite the criticism, the Japanese Naval Underground Headquarters is a good learning site. It allows visitors to see the caves without getting dirty or facing any of the dangers inherent in exploring such World War II caves. Without it, there would be no way for most people on Okinawa to understand some of the conditions of the battle.

To reach the Japanese Naval Underground Headquarters, head south on Highway 58 from Camp Foster. After passing over Meiji Bridge (just before the airport exit), Highway 58 becomes Highway 331. Just after the Banyan Tree Restaurant and the park, turn left on Highway 7. Follow the signs for the Japanese Navy Underground Headquarters. Parking is available in two lots.