The Peerless Superfortress
The Superfortress had no peer during the war among propeller-driven bombers. It compared favorably with the only operational turbojet bomber, Germany’s impressive Arado Ar 234 Blitz (Lightning) in speed at altitude, and was markedly superior in service ceiling (the highest an airplane can climb while still flying horizontally) and ferry range (the farthest distance a fully equiped airplane without payload can fly).
To the observer aboard the B-29, it shouts "American" in every direction, for the impression is of substantial size, great strength, overflowing technology, and assurance that this warplane can take on any foe and win. B-29 crewmen enjoyed (if that’s correct in a combat setting) a relatively spacious working environment with standup room for all, except for the tail gunner, especially when compared to its older sibling, the cramped B-17 Flying Fortress. Cabin pressurization, heating, and air conditioning added to the crew’s comfort.
Requirements for a High Performance Bomber
In the late 1930s, the Army Air Corps (AAC) began a search for a new high performance bomber that would stretch the state of the art of airplane design. During January 1940 the AAC issued a specification for a very heavy bomber with these requirements: 400 mph speed, high altitude capability with pressurized crew compartment, 5,000+ mile range with bomb load, defensive armament, and tricycle landing gear.
In order to attain the AAC desired top speed, Boeing proposed an aerodynamically clean, unarmed bomber, which would rely on its high speed and altitude capability as defense against enemy fighters. The AAC insisted on a fully armed pressurized bomber, which then led to remote controlled gun turrets, since open doors (resembling those on the B-17) were not compatible with pressurization. Fully armed B-29s did not meet the speed requirement, but the later Bell-built B-29B and Martin-built atomic bombers, which were shorn of all turrets and sighting blisters, except the tail turret and its guns, attained more than 400 mph.
Boeing and Consolidated Win Contracts
Boeing’s model 345 was chosen as the most promising of the designs submitted; a development contract for two XB-29 prototypes was issued on August 24, 1940. So high was the confidence of the AAC and especially its commanding officer General Arnold in Boeing’s ability that by time the XB-29 flew, 1,664 production airplanes were on order.
Consolidated’s B-32 Dominator served as a backup should the Superfortress fail. It flew several weeks before the B-29, used the same engines, was among the first airplanes with reversible pitch propellers, but its overall performance was lower. In the absence of cabin pressurization in production aircraft, all gun turrets were manned. The Dominator flew late war combat missions, but did not participate in the strategic bombing of Japan. It flew several photoreconnaissance sorties over Japan after the atomic bombs were dropped. Production totaled 118 aircraft of all models.
B-29 Design Features
An aerodynamically efficient high aspect ratio (long, narrow) wing with tightly cowled engines was joined to a streamlined, tapered fuselage surmounted by a large vertical tail. Eleven crewmen were housed in three pressurized compartments, the nose, waist, and tail turret sections. A communications tube (approximately 28-inches diameter x 35-feet long) through which crewmen could crawl joined the nose and waist compartments. Four waist area crew rest bunks were an original design element that was replaced by the radar operator’s station when navigation/bombing radar equipment was added.
Cabin pressurization enabled the B-29 to over-fly most of Japan’s defenses. Some late war Superfortress models flew above 40,000 feet altitude where they were invulnerable to attack. The B-29 built upon the earlier pressurization system Boeing developed for its 307 Stratoliner airliner, being the first mass production pressurized (by design) airplane and bomber. This key technology, perfected by the U.S. during World War II, would stand Boeing and America in good stead during the post war airliner boom, when it became essential. Much of Boeing's success today as a jet airliner manufacturer can be attributed to its pressurization expertise.
Wood was utilized for worktables, ladders, and floors, doubtless due to the Superfortress’ Pacific Northwest origin.
Powerful, Troublesome Engines
Wright Aeronautical provided the B-29 with four R-3350 Duplex Cyclone radial engines, which were then the most powerful, at 2,200 hp. Each engine was equipped with twin General Electric turbo-superchargers, which enabled the R-3350 to maintain maximum power up to 30,000 feet altitude, giving the Superfortress both high altitude and high-speed-at-altitude capability. However, engine fires dogged the B-29 during its early service. Magnesium (used in pyrotechnics it burns with a white searing flame) in engine and airframe components exacerbated the problem.
Defensive Guns Directed by Electro-Mechanical Computers
Fully armed B-29 versions featured five gun turrets -- upper forward and aft, lower forward and aft, and a manned tail turret. Each turret mounted two guns, except for the upper forward, which had four. All turrets were electrically powered (the B-29 was an electric airplane with more than 100 electric motors, including landing gear actuation), remotely sighted and controlled (no in-flight gunner access, including the tail turret), electro-mechanical computer directed, with manually fired guns.
General Electric developed the Central Fire Control system, which consisted of five interconnected electro-mechanical analog computers, one per gun turret. Each gunner could directly fire his own guns if the computer system was inoperative. All gunners had control of their turret and secondary control of others -- an intercom system provided communication between the gunners. A gunner could fire the guns of another turret from his sighting position, and, uniquely, fire the guns of two or more turrets at once.
Thousands of these computers were manufactured for and utilized by B-29s. This program, then, represents the first mass production and use of electronic computers, although they included mechanical components and thus were not purely "electronic."
The defensive armament system proved successful in combat, and was exclusive among the combatants during the war. On January 27, 1945, the B-29 identified as "B-29 A Square 52" scored 14 kills over Tokyo, Japan, as follows: rammed by two fighters, gunners then shot down 12 more fighters, the damaged bomber flew 1,500 miles back to Saipan on three engines, crash landed, all crewmen survived, but the aircraft was written off. This is probably the highest number of air-to-air kills by a single airplane during one mission.
B-29 Combat Missions
To introduce the B-29 into combat, bombers were based in India to strike at Japanese targets in Indochina. Combat operations began on June 5, 1944, with the bombing of Bangkok, Siam (Thailand). In order to bomb Japan itself, Chinese staging bases were prepared. To mount a mission from China, the B-29s had to first ferry their supplies from India over the "Hump" to China. When sufficient material was accumulated, the B-29s struck Japan from their Chinese bases. These attacks were ineffective and costly.
With the capture of the Pacific Mariana Islands group from the Japanese, a much better venue from which to launch B-29 raids against Japan was available. The Marianas were closer, and the Navy brought in the necessary supplies. Five huge airbases were built on the islands of Tinian, Saipan, and Guam.
The first raids on Japan were doctrinaire high altitude, precision-bombing missions, for which the B-29 had been expressly designed. They only minimally affected Japan’s war production capacity. A change in leadership put General Curtiss LeMay in command, he soon switched tactics. Low altitude, area bombing with unarmed B-29s dropping firebombs on Japanese cities proved highly successful. These attacks were the most destructive in history, atomic bombing included, leveling cities and crippling their war manufacturing efforts.
The two atomic bombs dropped by B-29s on Japan remain the only ones ever used in warfare. On August 6, 1945, a B-29 named Enola Gay bombed Hiroshima. Three days later, without a Japanese offer of surrender, a B-29 named Bockscar bombed Nagasaki. Contrary to popular belief these attacks did not end the war.
It continued unabated with the largest B-29 force of 828 bombers striking on August 14, 1945. Even after the Japanese agreed to the cease fire of August 15, fighting continued until August 18, when the last action probably occurred. Japanese fighters attacked two B-32 photo aircraft flying over Tokyo, two crewmen were wounded and one was killed.
Deadly Warplane had a Humanitarian Side
The B-29, while functioning as a deadly warplane to its enemies, had a humanitarian aspect to its missions. Probably unique in the annals of war, Superfortress’s dropped leaflets over Japan, listing the cities to be bombed next, thus some residents could and doubtless did escape harm. B-29s nicknamed Super Dumbos provided an ocean search and rescue service for their downed brothers. After the war, B-29s dropped food and clothing to inmates of prisoner of war camps.
The Soviet Union's Bootlegged B-29
Toward the end of the war the Soviet Union observed the massive destruction visited on Germany and Japan by Allied bombers. Lacking an equivalent aircraft, the U.S.S.R. set out to reproduce what it considered the best bomber, namely the B-29. Soviet forces had access to the latest German turbojet and rocket aircraft, but the B-29 was the only manned aircraft copied (the U.S. reproduced the German V-1 Buzz Bomb missile during the war, but did not employ it).
Fortunately for the Russians, three B-29s fell into their hands during the war, and from these pattern aircraft, Soviet designers reverse-engineered a near replica designated the Tupolev Tu-4. An entire aircraft industry segment was created to produce the very advanced airframe, engine, electrical and electronic components needed for it. More than 800 production aircraft were built.
B-29s in the Korean War
The B-29 fought again during the Korean War, in which the enemy used both propeller driven and very fast turbojet fighters in attempts to stop its bombing raids. The bombers were updated with more powerful engines, reversible pitch propellers, and other enhancements. B-29s were in action on all but 26 days during the war, some 35 months of combat, with a relatively small force of just over 100 bombers. Nonetheless, a bomb tonnage was dropped on Korean targets, almost equal to that during the earlier Pacific campaign. Smart bombs were dropped on Korean targets; radio guided Razon and giant Tarzon (12,000 lb.) weapons knocked down bridges successfully.
B-29s flew day and night missions accompanied by escorting fighters, but Mig-15 turbojet fighters (only) downed some of the big bombers, while taking losses from their defending guns. In a notable action, three Mig-15s were shot down by a single bomber, which survived the war, and later accounted for two more Mig-15s.
Mother Ship to the Supersonic Airplane
A Superfortress was instrumental to the first successful manned supersonic airplane flight. On October 14, 1947, a B-29 mother ship carried the Air Force Bell XS-1 rocket engine research aircraft (a World War II design) to launch altitude. After release from the B-29, Captain Chuck Yeager piloted the XS-1 to 700 mph/Mach 1.06. Interestingly, the Soviets used their Tu-4s and captured B-29s as mother ships in a similar research program.
The End of Active Service
On June 21, 1960, the B-29 flew its last mission for the Air Force, but the design lives on today in the Russian Tupolev Tu-20 Bear bomber, whose defensive gun system was derived from B-29s captured during World War II. Communist China evidently still flies Tupolev Tu-4s, modified with turboprop engines and a radar rotodome, in the airborne early warning role.
Three manufacturers built 3,960 Superfortresses in five factories. Boeing’s Seattle, Renton, and Wichita plants completed 2,766 aircraft, 70 percent of the total. The Renton facility, today the home of Boeing's single aisle jet airliners, built the last B-29 on May 28, 1946.
Time flies. Come September, the Superfortress will be 60!