[1] The entire system has a land area of 1.8 km² (455 acres) at high-tide, and is less than 2.5 miles (4.0 km) at its widest point.

Japan used the southern part of Pingelap Island during hostilities in the Pacific Ocean theater of World War II for a supply base.

The presence of foreign troops on the island led to the introduction of a number of infectious diseases, including gonorrhoea, tuberculosis and dysentery, which reduced the population from its pre-war level of around 1000 to 800, and decreased the fertility rate significantly.

Universal primary education was provided for Pingelapese children and a limited health care scheme was set up to eradicate the diseases introduced during the war.

[8] By generation six, the incidence rose to approximately 4.9%,[7] due to the founder effect and inbreeding, with all achromats on the island nowadays tracing their ancestry to Doahkaesa Mwanenihsed.

It is reported that one Pingelapese island sea-fisherman with this condition has difficulty seeing in bright sunlight, but at night can see in much fainter light than people with normal vision can; he uses this ability in a boat at night waving a large burning torch about to attract or confuse flying fish, which he then catches; the flying fish act as if the torch is the moon.