The worst fear of military leaders was that the considerable Japanese population of Hawaii would join forces with Japan in a land invasion of the islands or aid the enemy through acts of espionage or sabotage.

“Japanese loyalty became the burning question of the day,” regardless of whether they were American citizens, wrote Lt. Col. Thomas H. Green, who was in charge of the daily operations of the military government under martial law. Local Germans and Italians were also suspects, but Japanese made up more than a third of the population in Hawaii and were considered a sizable threat.

The fear that local Japanese would betray the U.S. fueled plans to evacuate Oahu Japanese to another island or the mainland and to hold them in detention camps. Under suspicion were those on an FBI watchlist, as well as all the Buddhist and Shinto priests, journalists, Japanese consular agents, language-school teachers, community leaders and even commercial fishermen.

With the writ of habeas corpus suspended under martial law on the day of the Pearl Harbor attack, 1,330 Japanese in Hawaii were eventually interned in detention camps within the territory or on the mainland. About 100 Germans and Italians were also interned.

Families were ripped apart with no explanation of why their relatives — all but eight were male — were suspected and where they would be detained, and many people didn’t know whether their loved ones were alive long after they were arrested, according to the Japanese Cultural Center of Hawaii.

There were a total of 17 internment camps on all the major islands, including converted prisons and military camps that kept smaller numbers of people for shorter periods of time. Places like the Lihue Plantation Gymnasium and Hilo Japanese Language School were used, the JCCH said. There were discrepancies in how internees were treated, depending on the personalities of camp commanders and guards, but conditions were harsh and primitive in the first weeks of chaos after the attack.

The Sand Island Detention Camp in Honolulu was activated a day after the attack, housing internees in tents for months until barracks were built. In 1942 the Army moved Sand Island internees to mainland camps, giving family members of interned men the option to accompany them.

More than 1,000 wives and children joined their loved ones, bringing the total number of Japanese from Hawaii interned during the war to 2,270, according to the JCCH.

The Honouliuli Internment Camp, the largest and longest-used camp, opened in March 1943 in pineapple fields off Kunia Road in Central Oahu. It was dubbed “Hell Valley” by detainees primarily because its location in a gulch trapped heat and moisture.

The 160-acre camp was surrounded by barbed wire and watched over by armed guards, according to the JCCH. The camp was built to hold 4,000, including prisoners of war from the Atlantic and Pacific.

Decades later in February 2015, Honouliuli was designated a national monument. It was called “Hawaii and America’s secret shame” by Secretary of the Interior Sally Jewell at an opening ceremony.

On the mainland, 117,000 Japanese in California and Oregon were relocated and detained under the authority of Executive Order 9066 of 1942.