The Boeing B-29 heavy bomber. To me the Boeing B-17 Flying Fortress, Consolidated B-24 Liberator and Being B-29 Superfortress were a series. The B-29 was huge, futuristic, pressurized, cylindrical, later left unpainted for better speed and altitude, designed for ETO, but fought in PTO only, four x 2 .50 cal remote gun turrets, etc. I think some of these were stripped out later, permitting even higher altitude flights and/or larger payloads. But there were also low-level night-time flights. I'm sure you all can add more about this.
B-29s made the necessary/needless/tragic (depending on one's perspective) war shortening/war ending atomic bomb attacks on August 6, 1945 on Hiroshima and August 9, 1945 against Nagasaki. Enola Gay bombed Hiroshima and was advance weather recon aircraft for Nagasaki. Bockscar bombed Nagasaki. These two aircraft are pictured here. A third B-29 named The Great Artist flew observation for both missions. Enola Gay's defensive armament was only two .50 cal guns. Top speed 339 mph. Crew 12. 2,200 hp.
Dave P. Muprhy adds: "When General LeMay took over command of The B-29 force bombing Japan, he did a similar shakeup as he had done in the ETO. This eventually resulted in a deletion of the external defensive turrets, switching over from HE bombs to incendiaries, and reducing the bomb release altitudes to as low as 7,000 feet. At the same time, B-29s were being used to deliver air-delivered naval mines (usually the Mark 13). The Mark 13 mines took a terrible toll on Japanese shipping. As designed, the tail stinger had a pair of .50-cal. machine guns joined with a single 20-mm cannon. The 20-mm cannon had reliability problems and many crews downloaded the weapon. The Silverplate B-29s had 1,000 rounds for each tail gun."