only wide. There was therefore no possibility of defence in depth, and the Japanese planned to counter-attack the landing beaches. They had not realized until the battle of Tarawa that American amphibious vehicles could cross coral reefs and land on the lagoon side of an atoll; accordingly the strongest defenses on Kwajalein faced the ocean. The bombardment by the Southern Attack Force, including the battleship , plus B-24 bombers from Abemama and artillery on Carlson island was devastating. The Navy had changed its bombardment tactics based on the Tarawa experience and used armor-piercing shells as well as firing into the island at closer ranges. The Official U.S. Army history of the battle quotes a soldier as saying "the entire island looked as if it had been picked up 20,000 feet and then dropped." Landing beaches Red 1 and 2 were assaulted at 0930 on 1 February, the Americans reaching halfway across the runway by sunset. Although the Japanese counterattacked every night, the island was declared secure by the end of the fourth day. On the north side of the atoll, the 4th Marine Division followed a similar plan, first capturing islets Ivan, Jacob, Albert, Allen, and Abraham on 31 January, and then landing on Roi-Namur on 1 February. The airfield on the western half (Roi) was captured quickly, and the eastern half (Namur) fell the next day. The worst setback came when a Marine demolition team threw a satchel charge of high explosives into a Japanese bunker, not realizing it was a torpedo warhead magazine. The resulting explosion killed twenty Marines and wounded dozens more and caused an observation pilot to radio, "The whole damn island has blown up!" Aftermath The relatively easy capture of Kwajalein demonstrated US amphibious capabilities and showed that the changes to training and tactics after the costly battle of Tarawa had been effective. It allowed Nimitz to speed up operations in the Marshalls and invade Ebeye Island on 3–4 February, Engebi Island on 18–19 February, Eniwetok Island on 19–21 February, and Parry Island on 22–23 February 1944. The Japanese also realized that beach-line defenses were too vulnerable to naval and aerial bombardment. In the campaign for the Mariana Islands, the defense in depth on Guam and Peleliu would be much harder to overcome than the comparatively thin line on Kwajalein. After the war ended, over 150 still operational US aircraft were sunk near Roi-Namur, which