STRAIT OF HORMUZ — The Strait of Hormuz remains effectively closed after the United States and Iran imposed competing naval blockades on the waterway, which once carried roughly a fifth of the world's oil and gas.

Naval blockades are a form of warfare that require no ground troops or invasion, only the ability to cut off what an enemy needs to survive.

Israel has imposed a complete land, sea and air blockade of the Gaza Strip since 2007, limiting the entry of goods and essential supplies. The blockade has caused a humanitarian and economic crisis for the territory's 2.3 million people, who cannot travel freely. Since 2010, all flotillas attempting to break the Gaza blockade have been intercepted or attacked by Israel in international waters. On April 30, 2026, Israel raided 22 of the 58 vessels in the most recent Global Sumud Flotilla campaign in international waters more than 1,000 km from Gaza.

The Nigerian federal government imposed a land, sea and air blockade on the Republic of Biafra shortly after it declared independence in July 1967. The blockade led to widespread starvation, causing an estimated one to two million deaths from hunger and disease rather than direct conflict, and ended with the Biafran surrender in January 1970.

The Beira Patrol was a nine-year blockade by the British navy, enforced under United Nations sanctions following Rhodesia's unilateral declaration of independence, to prevent oil from reaching Rhodesia through the Mozambican port of Beira. Rhodesia continued receiving oil via South Africa and other Mozambican ports not covered by the UN resolution. The patrol tied up 76 naval ships over nine years, with two frigates required on station at all times, and ended in July 1975 when Mozambique's independence allowed it to commit to blocking oil transit to Rhodesia.

In October 1962, the U.S. ordered a naval quarantine of Cuba after U-2 spy planes discovered Soviet nuclear missile sites under construction on the island. The U.S. called the measure a "quarantine" rather than a blockade to avoid a legal act of war, establishing a line 500 nautical miles (920 km) from Cuba's coast and authorizing warships to stop, search and turn back any vessel carrying offensive weapons. Nikita Khrushchev called the blockade "outright piracy" and an act of aggression. An agreement was reached for the Soviets to dismantle their offensive weapons in Cuba in exchange for a U.S. public declaration not to invade Cuba and a secret agreement to remove U.S. Jupiter missiles from Turkey. The quarantine formally ended on November 20, 1962, after all offensive missiles and bombers had been withdrawn.

During the Korean War, UN naval forces led by the U.S. imposed a blockade of the North Korean port of Wonsan in February 1951, aiming to deny the North Korean navy access to a city with a large harbour, airfield and petroleum refinery. The blockade forced North Korean and Chinese forces on the east coast to divert thousands of troops and artillery pieces away from the front line. The blockade lasted 861 days, ending with the signing of the Korean Armistice Agreement in July 1953.

The U.S. imposed a submarine blockade against Japan during the Pacific War beginning in 1942, combining attacks on Japanese merchant shipping with minelaying operations. U.S. submarines sank approximately 1,300 Japanese merchant ships and roughly 200 warships over the course of the war.