Question: Why were Niihau's residents unaware of the attack on Pearl Harbor?
About the article "Attack on Pearl Harbor", section "Niihau Incident".

Candidate passages:
The results of the attack on Pearl Harbor are many and significant. 
The Japanese planners had determined that some means of rescuing fliers whose aircraft were too badly damaged to return to the carriers was required.
The island of Niihau, only 30 minutes flying time from Pearl Harbor, was designated as the rescue point.
The Zero flown by Petty Officer Shigenori Nishikaichi of Hiryu was damaged in the attack on Wheeler, and he flew to the rescue point on Niihau.
The aircraft was further damaged on landing.
Nishikaichi was helped from the wreckage by one of the native Hawaiian inhabitants, who, aware of the tension between the United States and Japan, took the pilot's maps and other documents.
The island's residents had no telephones or radio and were completely unaware of the attack on Pearl Harbor.
Nishikaichi enlisted the support of three Japanese-American residents in an attempt to recover the documents.
During the ensuing struggles, Nishikaichi was killed and a Hawaiian civilian was wounded; one collaborator committed suicide, and his wife and the third collaborator were sent to prison.
The ease with which the local ethnic Japanese residents apparently went to the assistance of Nishikaichi was a source of concern for many, and tended to support those who believed that local Japanese could not be trusted.
Prior to the unification of the Kingdom of Hawaii under Kamehameha I, Niihau was ruled by the "alii".
Kahelelani was the first of the Niihau alii.
His name is now used to refer to the "Niihau kahelelani", the puka shell of the wart turbans ("Leptothyra verruca"), used to make exquisite Niihau shell jewelry.
Kāʻeokūlani was a ruler of northern Niihau who unified the island after defeating his rival, a chief named Kawaihoa.
A stone wall (Pāpōhaku) across a quarter of the island's southern end marked the boundaries of the two chiefs: Kāeo's land was identified by black stones and Kawaihoa's by white stones.
Eventually, a great battle took place, known as Pali Kamakaui.
Kāeo's two brothers from the island of Maui, Kaiana and his half-brother Kahekili II, the King of Maui, fought for Kāeo and Niihau was united under his rule.
Kawaihoa was banished to the south end of the island and Kāeo moved to the middle of the island to govern.
Kāeo married the Queen Kamakahelei and a future king of Niihau and Kauai named Kaumualii was born in 1790.
Kauai and Niihau are said to have carried the "highest blood lines" in the Hawaiian Islands.
Kamehameha managed to unify all of the islands by 1795, except for Kauai and Niihau: Two attempts to conquer those islands had failed, and Kamehameha lost many men: bodies covered the beaches on Kauai's eastern shores.
Finally, in 1810, Kamehameha amassed a great fleet, and Kaumualii, the last independent "alii", surrendered rather than risk further bloodshed.
Independence again became feasible after Kamehameha's death in 1819, but was put down when Kamehameha's widow Kaahumanu kidnapped Kaumualii and forced him to marry her.
Thereafter Niihau remained part of the unified Kingdom of Hawaii.
Elizabeth McHutchison Sinclair (1800–1892) purchased Niihau and parts of Kauai from Kamehameha V in 1864 for $10,000 in gold.
Sinclair chose Niihau over other options, including Waikīkī and Pearl Harbor.
By around 1875, Niihau's population consisted of about 350 Native Hawaiians, with 20,000 sheep.
This era marked the end of the art of Hawaiian mat–weaving made famous by the people of Niihau.
"Makaloa" ("Cyperus laevigatus"), a native sedge, used to grow on the edges of Niihau's three intermittent lakes.
The stems were harvested and used to weave "moena makaloa" (mats), considered the "finest sleeping mats in Polynesia".
The mats were valued by "alii" and foreign visitors alike, but by the end of the 19th century, Hawaiians had stopped weaving "makaloa" due to changes in population, culture, economics, and the environment.
In 1915, Sinclair's grandson Aubrey Robinson closed the island to most visitors.
Even relatives of the inhabitants could visit only by special permission.
Upon Aubrey's death in 1939 the island passed to his son Aylmer, and in 1968 to Aylmer's youngest brother Lester.
Upon Lester's wife Helen's death, the island passed to his sons Bruce and Keith Robinson, the current co-owners.
(See Owners' family tree)Niihau played a small role during the attack on Pearl Harbor on December 7, 1941.
In what has come to be called the Niihau Incident (or the Battle of Niihau), an off-course Japanese pilot crash-landed on the island and was captured by locals.
The pilot escaped with the assistance of local Japanese residents, but was later recaptured and killed.
Despite its self-imposed isolation, Niihau has a long-standing relationship with the U.S. military dating from 1924.
There is a small Navy installation on the island.
No military personnel are permanently stationed there, but the U.S. military has used the island for training special operations units, which included hiring Hawaiians that live on Ni'ihau as "enemy" trackers. 
Military Service.
World War II.
Pearl Harbor.
During Pearl Harbor, Lieutenant Powell's first assignment with the United States Army Air Corps was to the 78th Pursuit Squadron located at Wheeler Field in Hawaii.
On December 7 during the Japanese attack on Pearl Harbor, Lt. Powell was a flight leader, however, all his squadron's aircraft were either damaged or destroyed during the attack.
Therefore, no members of his squadron were able to get airborne during the attack on Pearl Harbor. 
Pearl Harbor is a lagoon harbor on the island of Oahu, Hawaii, west of Honolulu Joint Base Pearl Harbor-Hickam, the joint United States Navy and Air Force base in Oahu   Attack on Pearl Harbor, the 7 December 1941 Japanese attack on the American naval base  Pearl Harbor National Wildlife Refuge Pearl Harbor may also refer to: