YOKOHAMA, Japan — On a hillside overlooking an athletic field where high school students play volleyball, an inconspicuous entrance leads down a dusty, slippery slope — and seemingly back in time — to Japan’s secret Imperial Navy headquarters during the final months of World War II.
Here, leaders of Japan’s combined fleet command made plans for the fiercest battles, including those of Leyte Gulf, Iwo Jima, and Okinawa, from late 1944 to the war’s end in August 1945. They knew that kamikaze pilots had crashed to their deaths when signals from their planes stopped. They wept over cables from officers aboard the famed battleship Yamato as it came under heavy US fire and sank off southern Japan.
Today, the barren, concrete tunnels sit quietly underneath a high school and university campus, largely untouched and unknown, occasionally visited by guided tours for the students. This week, the school opened them to the news media for the first time to raise public awareness of the site, and the tragic history it represents, in the 70th anniversary year of the end of World War II.
‘‘It’s a negative heritage that humans made. It’s the perpetrators’ legacy,’’ said Takeshi Akuzawa, assistant headmaster of Keio Senior High School, who escorted the media tour Tuesday. ‘‘Just imagine the massive number of people who had to die in the final year of the war because of their operations.’’
The inverted U-shaped tunnels are a silent reminder of a time when students and many others were sent to war, many to their deaths, under orders that emanated from this bunker under a school.
Experts say its significance is increasing, especially as that era fades from memory and there is a growing reluctance among some Japanese to look at the negative side of their country’s history.
One of Japan’s top universities, Keio leased the site to the navy in 1944 under an Education Ministry order after thousands of teachers, staff, and students were drafted into the military, leaving the campus virtually empty. Above ground, the navy commanded from a dormitory, rushing to the underground center whenever US B-29 bombers flew over.
Keio’s Hiyoshi campus, south of Tokyo in Yokohama, was chosen apparently because of its relative proximity to both the Yokosuka naval base and command headquarters in Tokyo. The hilltop campus also was suitable for an underground facility.
Construction of the underground tunnels began in July 1944, performed by troops and forced laborers from Korea. A room for the chief commander, Admiral Soemu Toyota, and key departments were ready in a few months.
In the chief commander’s room, unlike elsewhere in the underground complex, cement on the walls was smoothed out, the floor was covered with tatami mats, and there was a door. His room was slightly elevated so the floor remained dry, and there was even a flush toilet.
The tunnel command center also had ventilation ducts, a battery room, and food storage with an ample stock of sake, in addition to deciphering and cable and communications departments. Marks on the ceiling remain from the overhead lights. The tunnels housing the command center and its facilities are 100 feet underground, and cover about 1.6 miles.
The conditions for those leading the war contrasted with those of ordinary people, who hid in small mud shelters as firebombs rained down from the sky, Akuzawa said.
Hisanao Oshima, who was there from February to May 1945 on a communications crew monitoring Morse code, still cannot forget the moments when he lost signals from kamikaze fighters. ‘‘The sound stops, and that means he crashed. I just cannot get that out of my head,’’ he said in an interview with public broadcaster NHK.
This site must be preserved ‘‘so that we can say it’s the proof why we should not wage war ever again,’’ Oshima said.
Japan also built the Matsushiro Imperial Underground Headquarters in central Japan for then-Emperor Hirohito and Imperial Army and key government officials, as they prepared for a possible ground war with the Americans, though that one was never used.
Hundreds of hangers, tunnels, and other wartime remains still exist in Japan, but many have been abandoned as interest has waned.