One day his vehicle struck an explosive device. When he regained consciousness, he said, he saw that shrapnel had gouged his right leg, shredded his gunner’s belly, and sliced into his commander’s left arm.

Treatment helped him complete the tour. But he eventually lost feeling in the leg and was incapacitated by anxiety and depression.

By the time he was discharged in 2018, he could not tolerate crowded areas, so he sought refuge in the Marshall Islands. But even there, his condition, he said, forces him to isolate from family.

Traveling to “the mainland,” as many Marshallese refer to the United States, to refill his prescriptions can be prohibitively expensive. Mr. Jermeto, whose main source of income is a disability benefit, can catch a free military flight from a nearby American base to Honolulu, but a round-trip flight from his home to the base costs about $500. The military flight is also often full, and. Hotels and food in Hawaii can cost hundreds more.