While it is not known how many people inhabited the island, the lack of freshwater probably limited the population to a few hundred. As many as 100 or more people may have once lived at Hakioawa, the largest settlement located at the northeast end of the island facing Maui.
Violent wars among competing chiefs laid waste to the land and led to a decline in the population. During the War of Kamokuhi, Kalaniopuu, the ruler of the Island of Hawaii, raided and pillaged Kahoolawe in an unsuccessful attempt to take Maui from Kamalalawalu, the King of Maui. From 1778 to the early 1800s, observers on passing ships reported that the island was uninhabited and barren, destitute of both water and wood. After the arrival of missionaries from New England, the Hawaiian government of King Kamehameha III replaced the death penalty with exile, and Kahoolawe became a male penal colony sometime around 1830. Food and water were scarce, some prisoners reportedly starved, and some swam across the channel to Maui to find food. The law making the island a penal colony was repealed in 1853.
An 1857 survey of Kahoolawe reported about 50 residents, about of land covered with shrubs, and a patch of sugar cane. Along the shore, tobacco, pineapple, gourds, pili (pee-lee) grass and scrub trees grew. Beginning in 1858, the Hawaiian government leased Kahoolawe to a sequence of ranching ventures. Some proved more successful than others, but the lack of freshwater was an unyielding enemy. Through the next 80 years, the landscape changed dramatically—drought and uncontrolled overgrazing denuded much of the island, and strong trade winds blew away much of the topsoil leaving the red hard pan.
From 1910 to 1918 the Hawaiian Territorial government designated Kahoolawe as a forest reserve in hopes of restoring the island through a revegetation and livestock removal program. The program failed and leases again became available. In 1918, the skilled Wyoming rancher Angus MacPhee with the help of Maui landowner Harry Baldwin leased the island for 21 years, intending to build a cattle ranch. By 1932, the ranching operation was enjoying moderate success. After heavy rains, native grasses and flowering plants would sprout, but drought seemed to always return. In 1941, MacPhee subleased part of the island to the Army. Later that year, because of continuing drought, MacPhee removed his cattle from the island.
On December 8, 1941, after the Japanese attack on Pearl Harbor, the U.S. Army declared martial law throughout Hawaii and took control of Kahoolawe. Soon, Kahoolawe was being used as a place to train Americans headed to war across the Pacific. The use of Kahoolawe as a training range was believed to be critical to the lives of many young Americans. The United States was executing a new type of war in the Pacific islands. Success depended on accurate, heavy gunfire from ships suppressing enemy positions as Marines and soldiers struggled to get ashore. Thousands of soldiers, sailors, Marines and airmen prepared on Kahoolawe for the brutal and costly assaults on islands such as the Gilberts, the Marianas and Iwo Jima.
Training on Kahoolawe continued after World War II. During the Korean War, carrier-based aircraft played a critical role in attacking enemy airfields, convoys and troop staging areas. Mock-ups of airfields, vehicles and other camps were constructed on Kahoolawe, and while pilots were undergoing readiness inspection at nearby Barbers Point Naval Air Station, they practiced spotting and hitting the mock-ups at Kahoolawe. Similar training took place through the Cold War and during Vietnam, as mock-ups of aircraft, radar installations, gun mounts and surface-to-air missile sites were placed across the island for pilots and others to use for training.
In early 1965, the United States Navy conducted Operation Sailor Hat to determine the blast resistance of ships. Three tests off the coast of Kahoolawe subjected the Island and a target ship to massive explosions, with 500 tons of conventional TNT detonated on the Island near the target ship USS Atlanta (CL-104); The ship was damaged, but not sunk. The blasts created a crater on the island known as "Sailor Man's Cap", cracking the small fresh water well on the island rendering it incapable of holding fresh water and making the Island all but uninhabitable.
In 1976, a group of individuals calling themselves the Protect Kahoolawe Ohana (PKO) filed suit in federal court to stop the Navy’s use of Kahoolawe for military training, to require compliance with a number of new environmental laws and to ensure protection of cultural resources on the island. In 1977, the Federal District Court for the District of Hawaii allowed the Navy’s use of the island to continue, but the Court directed the Navy to prepare an environmental impact statement and complete an inventory of historic sites on the island. On March 9, 1977, two PKO leaders, George Helm and Kimo Mitchell, were lost at sea during an attempt to occupy Kahoolawe in symbolic protest. In 1980, the Navy and the Protect Kahoolawe Ohana entered into a Consent Decree which allowed continued military training on the island, monthly access to the island for the PKO, surface clearance of part of the island, soil conservation, goat eradication and an archaeological survey.
On March 18, 1981, the entire island was added to the National Register of Historic Places. At that time, the Kahoolawe Archaeological District was noted to contain 544 recorded archaeological or historic sites and over 2,000 individual features. As part of the soil conservation efforts, workers laid lines of explosive charges, detonating them to break the hardpan so that seedling trees could be planted. Used tires were taken to Kahoolawe and placed in miles of deep gullies to slow the washing of red soil from the barren uplands to the surrounding shores. Ordnance and scrap metal was picked up by hand and transported by large trucks to a collection site.
In 1990, President George H. W. Bush ordered an end to live-fire training on the island. The Department of Defense Appropriations Act for Fiscal Year 1991 established the Kahoolawe Island Conveyance Commission to recommend terms and conditions for the conveyance of Kahoolawe by the United States government to the State of Hawaii.
As required by Title X, the Navy retained access control to the island until clearance and environmental restoration activities were completed, or November 11 2003, whichever came first. The State agreed to prepare a Use Plan for Kahoolawe and the Navy agreed to develop a Cleanup Plan based on that use plan and to implement that plan to the extent Congress provided funds for that purpose.
In July 1997, the Navy awarded a contract to the Parsons/UXB Joint Venture to clear ordnance from the island to the extent funds were provided by Congress. After the State and public review of the Navy cleanup plan, Parsons/UXB began their work on the island in November 1998.
The Navy attempted a cleanup of the unexploded ordnance from the island, although much still remains buried or resting on the land surface. Other items have washed down gullies and still others lie beneath the waters offshore. The turnover was officially made on November 11 2003, but the cleanup was not completed. Although the U.S. Navy was given $400 million and 10 years to complete the task, work progressed much more slowly than anticipated. As of the time of turnover, access to Kahoolawe requires escort and careful attention within areas known to contain unexploded ordnance.
The Legislature also created the Kahoolawe Island Reserve Commission (KIRC) to manage the Reserve while it is held in trust for a future Native Hawaiian Sovereignty entity. The restoration of Kahoolawe will require a strategy to control erosion, re-establish vegetation, recharge the water table, and gradually replace alien plants with native species. Plans will include methods for damming gullies and reducing rainwater runoff. In some areas, non-native plants will temporarily stabilize soils before planting of permanent native species.