Gua·dal·ca·nal (gwŏd'l-kə-nāl') A volcanic island of the western Pacific Ocean, the largest of the Solomon Islands. Visited by English navigators in 1788, the island became a British protectorate in 1893. It was occupied by the Japanese in World War II, leading to an invasion by U.S. troops in August 1942. After fierce jungle fighting, the island was captured by the Allies in February 1943.