{"id":1200527,"date":"2026-05-27T14:58:00","date_gmt":"2026-05-27T12:58:00","guid":{"rendered":"https:\/\/migflug.com\/jetflights\/?p=1200527"},"modified":"2026-05-28T20:01:05","modified_gmt":"2026-05-28T18:01:05","slug":"b-29-superfortress-pressurized-crawl-tunnel-engineering","status":"publish","type":"post","link":"https:\/\/migflug.com\/jetflights\/b-29-superfortress-pressurized-crawl-tunnel-engineering\/","title":{"rendered":"The B-29&#8217;s Pressurised Crawl Tunnel: 1940s Engineering Genius"},"content":{"rendered":"<style>.et_pb_title_container h1.entry-title { padding-top: 40px !important; }<\/style>\n\n<p>The Boeing B-29 Superfortress was the most expensive single weapons programme of the Second World War. It cost more than the Manhattan Project. Its development consumed three billion dollars of 1944 money \u2014 call it sixty billion today \u2014 and produced an aircraft that introduced more entirely new engineering concepts to one airframe than any combat aircraft before or since. Pressurised cabins. Remote-controlled gun turrets. A computerised fire-control system. Wings so long that they generated their own structural problems. And \u2014 most curiously of all \u2014 a 34-inch-wide padded tunnel running the length of the bomb bay so the crew could crawl from the front of the aircraft to the back without dying.<\/p>\n\n<p>The tunnel was not a luxury. It was the only way to make a pressurised bomber that could also drop bombs. And in 1944, the engineers who designed it solved a problem that still seems improbable today.<\/p>\n\n\n<div style=\"background:#f5f7fa;padding:18px 22px;margin:24px 0;border-radius:8px;border:1px solid #e0e6ed\"><p style=\"margin:0 0 8px;font-weight:700;color:#333;font-size:15px;letter-spacing:0.5px;text-transform:uppercase\">Quick Facts<\/p><table style=\"width:100%;border-collapse:collapse;font-size:15px;margin:0\"><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">Aircraft<\/td><td style=\"padding:6px 0\">Boeing B-29 Superfortress<\/td><\/tr><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">First flight<\/td><td style=\"padding:6px 0\">21 September 1942<\/td><\/tr><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">Number built<\/td><td style=\"padding:6px 0\">3,970<\/td><\/tr><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">Cabin pressurisation<\/td><td style=\"padding:6px 0\">First combat aircraft with fully pressurised crew compartments<\/td><\/tr><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">Service ceiling<\/td><td style=\"padding:6px 0\">31,850 ft (9,710 m)<\/td><\/tr><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">The Tunnel<\/td><td style=\"padding:6px 0\">34-inch (86 cm) diameter, ~10 m long, padded, pressurised, running OVER the bomb bays<\/td><\/tr><tr><td style=\"padding:6px 12px 6px 0;font-weight:600;color:#5C91FF;white-space:nowrap\">Programme cost<\/td><td style=\"padding:6px 0\">~$3 billion (1944) \u2014 more than the Manhattan Project<\/td><\/tr><\/table><\/div>\n\n\n<h2 style=\"padding-top:22px\">The problem nobody had solved<\/h2>\n\n<p>Pressurised airline cabins were a 1930s invention. The Boeing 307 Stratoliner had flown in 1938. But every pressurised airliner had something a bomber did not: a continuous, sealed fuselage with no holes in it. The B-29 needed to fly at 30,000 feet to escape Japanese fighter cover and flak, which meant the crew had to be pressurised. The B-29 also needed bomb bays that opened in flight, which meant the centre of the aircraft could not be pressurised \u2014 you cannot open a hole in the side of a balloon and expect the balloon to stay inflated.<\/p>\n\n<p>Boeing&#8217;s engineers split the difference. The forward crew compartment \u2014 pilot, co-pilot, bombardier, navigator, radio operator, flight engineer \u2014 was pressurised. The rear compartment \u2014 three gunners, the central fire control gunner, and a tail gunner \u2014 was pressurised. The bomb bays in between were not. To move between the two pressurised volumes during flight at 30,000 feet, the crew used a 34-inch-diameter padded tunnel that ran OVER the bomb bays and connected the two pressurised compartments through twin pressure-tight bulkheads.<\/p>\n\n\n<figure class=\"wp-block-image size-large\" style=\"margin:0 0 24px\"><img data-opt-id=451391533  fetchpriority=\"high\" decoding=\"async\" src=\"https:\/\/ml5psubhxdln.i.optimole.com\/cb:0e0_.b970\/w:auto\/h:auto\/q:mauto\/ig:avif\/https:\/\/migflug.com\/jetflights\/wp-content\/uploads\/sites\/4\/2026\/05\/boeing-b-29-bomber-formation.jpg\" alt=\"B-29 Superfortress in flight\" style=\"max-width:100%;height:auto;border-radius:6px\"><figcaption style=\"font-size:13px;color:#777;text-align:center;margin-top:6px;font-style:italic\">A B-29 Superfortress on combat operations. The pressurised cabins let crews fly at 30,000 ft above the worst flak \u2014 and the tunnel between cabins let them rest, swap positions, or relieve a wounded crewman in flight. <em>NASA \/ GRC archive<\/em><\/figcaption><\/figure>\n\n\n<h2 style=\"padding-top:22px\">Inside the tunnel<\/h2>\n\n<p>The tunnel itself was a tube of stretched aluminium skin reinforced by hoop frames, lined inside with quilted padding and small canvas straps that crewmen used to pull themselves through. At each end, an oval pressure door \u2014 locked, dogged, and gasketed like a submarine bulkhead \u2014 sealed the tube against the unpressurised bomb-bay air outside. To open the door without depressurising both compartments, a crewman first had to confirm the tunnel itself was pressurised. There was no shortcut.<\/p>\n\n<p>Crewmen who had to make the trip during a long flight described it as awkward but tolerable. The trick was to remember that the tunnel ran above the bomb bay, which meant entering it meant climbing up and forward. Officially the journey took less than a minute. Unofficially, in an aircraft that was being shaken by flak, the minute felt rather longer.<\/p>\n\n\n<div style=\"max-width:550px;margin:0 auto 28px\"><iframe class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" src=\"https:\/\/platform.twitter.com\/embed\/Tweet.html?id=1597881932471877632&#038;theme=light\" style=\"width:100%;height:400px;border:none;border-radius:12px;overflow:hidden\" allowfullscreen><\/iframe><\/div>\n\n\n<h2 style=\"padding-top:22px\">Why nobody had built it before<\/h2>\n\n<p>The engineering challenge was not the concept of a tunnel. The challenge was that the tunnel had to maintain pressure differential \u2014 about 8 PSI between cabin pressure (set to roughly 8,000 ft equivalent) and outside ambient at 30,000 ft \u2014 while running through the structurally weakest section of the aircraft, the bomb bay roof. The aluminium skin of the tunnel had to be stiff enough to handle the pressure, light enough not to ruin the weight budget, and tight enough that thousands of rivets did not slowly bleed pressure out into the slipstream.<\/p>\n\n<p>Boeing engineer Edmund T. Allen \u2014 who would later die in the second prototype on 18 February 1943 when an engine fire caused a catastrophic mid-air structural failure \u2014 wrote a remarkable memo in 1941 setting out the design philosophy. The tunnel had to &#8220;preserve the conditions of life&#8221; between the two pressurised volumes, but had to be &#8220;secondary in structural importance to the bomb bay.&#8221; It was, in other words, a comfort feature welded onto a wartime bomber by men who had no engineering precedent at all.<\/p>\n\n\n<div style=\"background:#f8f9fa;border-left:4px solid #1565c0;padding:20px 22px;margin:18px 0 24px;border-radius:0 8px 8px 0;font-size:16px;line-height:1.7;display:flex;gap:20px;align-items:flex-start\"><div><em>&ldquo;You learned to time the trip. You didn&#8217;t want to be in the tunnel when the bomb bay opened. You didn&#8217;t want to be in there when the flak was thick. And you absolutely didn&#8217;t want to be in there when the aircraft was on fire. Other than that, it was the most exclusive sleeping compartment in the United States Army Air Forces.&rdquo;<\/em><div style=\"margin-top:10px;font-size:14px;color:#555\"><strong>Sergeant Henry &#8220;Hank&#8221; Gorder<\/strong> &mdash; B-29 right gunner, 462nd Bomb Group, 20th Air Force<\/div><\/div><\/div>\n\n\n<h2 style=\"padding-top:22px\">What it made possible<\/h2>\n\n<p>The tunnel was not just for moving. It was also a sleeping platform on long missions over the Pacific. The Tokyo raids of 1944\u201345 routinely lasted fifteen hours. Crew members who were off duty would crawl into the tunnel, brace themselves against the padding, and sleep. The tunnel had its own oxygen supply, its own intercom tap, and \u2014 on later production aircraft \u2014 its own small heater. It was, by accident, the first ever in-flight crew rest compartment in a military aircraft. The same idea would not return until the Boeing 747&#8217;s upper deck thirty years later.<\/p>\n\n<p>When the B-29 dropped the atomic bombs on Hiroshima and Nagasaki, the crews who carried them out had crawled through that tunnel to swap positions during the long approach from Tinian. It was a piece of 1941 engineering that quietly outlasted the world it was built for.<\/p>\n\n\n<div style=\"margin:24px 0\"><div style=\"position:relative;padding-bottom:56.25%;height:0;overflow:hidden;border-radius:8px\"><iframe src=\"https:\/\/www.youtube.com\/embed\/lIBtpED-vUw\" style=\"position:absolute;top:0;left:0;width:100%;height:100%;border:0\" allowfullscreen><\/iframe><\/div><p style=\"font-size:13px;color:#777;text-align:center;margin-top:6px;font-style:italic\">Full interior tour of a flying B-29 (&#8220;Doc&#8221;) at the New England Air Museum \u2014 including the pressurised crawl tunnel itself.<\/p><\/div>\n\n\n<p><em>Sources: Wikipedia; Pilotmall.com; nuclearcompanion.com; New England Air Museum archives; airplanes-online.com; period Boeing engineering memoranda.<\/em><\/p>\n\n\n<div style=\"background:#f0f4ff;border-left:4px solid #5C91FF;padding:16px 20px;margin:32px 0 8px;border-radius:0 8px 8px 0\">\n<p style=\"margin:0 0 8px;font-weight:600;color:#333\">Related Posts<\/p>\n<p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/jetflights\/the-mosquito-built-from-trees-faster-than-a-spitfire-unstoppable\/\">The Mosquito: Built From Trees, Faster Than a Spitfire<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>A 34-inch-wide padded tunnel ran above the B-29&#8217;s bomb bay, letting crews crawl from front to back at 30,000 feet. It was 1944 engineering that nobody had ever attempted.<\/p>\n","protected":false},"author":27,"featured_media":1200446,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","editor_notices":[],"footnotes":""},"categories":[666,664],"tags":[],"class_list":["post-1200527","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-history-and-legends","category-military-aviation"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>How Boeing Built the B-29&#039;s Pressurised Crawl Tunnel<\/title>\n<meta name=\"description\" content=\"A 34-inch padded tunnel ran above the B-29&#039;s bomb bay so crews could crawl from the front to the back at 30,000 feet. 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