High Altitude Heavy Bomber for RAF

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While that's true, none of that affected the accuracy of the bomb detonation in relation to the aiming point. Of course the original aiming point was down on the shoreline at the Nagasaki docks some two miles away from where the bomb went off, but given the bomb was dropped visually, and the bomb aimer, "the Great Artiste" himself, only saw the race course that he decided he was going to use as the aiming point briefly through the clouds, the hypocenter was only a few hundred metres in horizontal distance from it. Again, it is a testament to the accuracy of the sight that the bomb detonated as close as it did to the aiming point.
 

Yep, there were a total of 46 Silverplate B-29s but only 15 were capable of carrying the nuclear weapons. Although the Silverplate programme was originally specifically designed for the Manhattan Project, it was to offer a greater range and increased altitude for a given bomb load for the type.
 
Frog said:
Project Silverplate (development and production of a special B-29 variant to deliver tha atomic bomb) was one of the sub-programs of the Manhattan project
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Only 15 of the Silverplate B-29s could carry nuclear weapons, while there were 46 Silverplate B-29s in total, the project grew beyond the nuclear requirement.
 

You're only partially right on this, the ten ton bomb requirement wasn't why Ramsay recommended the Lancaster in his report (in 1943 the Lancaster couldn't carry 10 tons), it was because it was the only aircraft that could carry the Thin Man bomb internally, which, not even the B-29 could do without modification. Only one B-29 was modified to carry Thin man, but the Lanc was rejected because when Arnold and Leslie Groves were told by Ramsay that it could carry the bomb, Arnold wanted the entire operation to be run by the Army Air Force, besides, he was backing the B-29 at a time when its engines were proving troublesome, threatening the project.

The Lancaster wasn't rejected because its bomb bay was too narrow, in fact the Lancaster's bomb bay, at 33 feet in length and five feet wide, was bigger and had a greater uninterrupted floor space than the B-29's two bomb bays, although the B-29's were deeper. This is why Ramsay mentioned it in his report. To carry Thin Man the space under the B-29's wing box had to be modified and this was done to only one, the 58th production aircraft, which was nicknamed "the Pullman B-29". Once Thin Man was cancelled and the Little Boy bomb was designed, there was no need to modify B-29s, as it was able to fit into the standard bomb bay length of the B-29 without modification, with two inches to spare, as was the Fat Man implosion bomb. As for a Lancaster carrying Fat Man, the Lancaster was never mentioned regarding that. Its only mention in any of the Manhattan Project paperwork is with reference to the Thin Man bomb, nothing else.

One aspect of the Lancaster that was carried through to the B-29 atom bomb raids was its bomb shackle. When trials were carried out with a dummy Thin Man in the bomb bay of the Pullman B-29, one of the four shackles, based on glider towing hooks failed and the bomb fell loose in the bomb bay. To avoid this happening again, one shackle was decided on and the British bomb shackle designed for carrying the Tall Boy bomb aboard the Lancaster was installed in the atom bomb carrying B-29s.
 
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The Avro Lancaster couldn't have delivered a Fat Man bomb from Tinian to Japan and returned safely.

Here's why:
The Lancaster's operational range with a heavy payload was around 1,660 miles (2,670 km). The round-trip distance from Tinian to Nagasaki is over 3,000 miles (4,800 km)—well beyond the Lancaster's capability with a 10,000+ lb bomb like Fat Man.

Fat Man was 128 inches long and 60 inches in diameter, weighing over 10,000 pounds. The Lancaster's bomb bay would have required major structural modifications to accommodate it—something that was already done for the B-29 Silverplate program.

The B-29 could fly higher and faster than the Lancaster, which was crucial for escaping the blast radius of a nuclear detonation.
So while the Lancaster was a phenomenal bomber in Europe—and even considered for atomic missions early on—it simply didn't have the range-payload-ceiling combination needed for the Pacific theater's unique demands.

The Avro Lancaster probably would not have survived delivering a Fat Man–type atomic bomb under the same conditions as the B-29 missions over Japan.

The Lancaster's service ceiling was around 24,500 feet, while the B-29 dropped Fat Man from 30,000 feet. That extra altitude gave the B-29 a better chance of escaping the blast and shockwave.

The B-29 was faster and had a better climb rate, which helped it clear the area more quickly after release. The Lancaster, being slower and flying lower, would have had less time to escape the detonation radius.

Fat Man had a blast yield of about 21 kilotons. Even with a parachute-retarded drop (which delayed detonation to give the aircraft time to escape), a lower-flying, slower aircraft like the Lancaster would have been at greater risk of damage or destruction from the shockwave.

So while the Lancaster could theoretically carry a large bomb like Fat Man (with modifications), it likely couldn't have delivered it safely from a Pacific base like Tinian and survived the mission. The B-29's combination of range, altitude, and speed made it uniquely suited for that role.
 

There's no way you could get a Fat Man bomb fitted to the Lancaster, the suggestion of it comes from internet fantasists who have said that it could based on the fact that Ramsey went to meet Roy Chadwick in Canada overseeing the opening of Lancaster production in Malton Ontario. During the visit, Ramsey showed Chadwick drawings on bomb shapes without telling him what they were specifically for, asking if the Lancaster could carry these, to which Chadwick said yes, without being given dimensions or weights. From this, people have made the leap to the Lancaster carrying the Fat Man bomb, which is a huge stretch. As I mentioned, the mention of the Lancaster in the Manhattan Project is confined to the Thin Man bomb in 1943.
 
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Internet fantasists have also said that the Lancaster could make the atom bombing trip from Tinian and back -- with in-flight refueling!

That claim definitely stretches the bounds of historical and technical plausibility.

While in-flight refueling was being experimented with during WWII, it was nowhere near operational or reliable enough to support a mission as complex and dangerous as an atomic bombing run from Tinian to Japan and back using Avro Lancasters.

Here's why that idea doesn't hold up:

Lancasters were not equipped for aerial refueling, nor were there tanker aircraft or procedures in place to support such missions at scale. The technology was still in its infancy and highly experimental.

Even if retrofitted, the logistics of refueling multiple heavy bombers midair over the Pacific—in wartime conditions, with nuclear payloads—would have been wildly impractical and dangerous.

The B-29 was chosen precisely because it didn't need refueling. Its range, ceiling, and speed made it uniquely suited for the atomic missions from Tinian without external support.

Some speculative discussions and documentaries have floated the idea of "Black Lancasters" or RAF involvement in atomic delivery, but these are largely what-if scenarios, not grounded in operational reality.
 

This is crucial, along with the range.
 
Alan Stevens said:
It was a close call with the B-29, with that diving 155 degree turn at 31,000 feet that pushed the structural limits to the max, and then the shock waves. No damage but they had little room to spare.
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I don't doubt the Lancs could handle the Gs -- I mean, they were doing corkscrews to dodge nightfighters over Europe -- but from 7,000 foot lower, you're cutting into safety padding in terms of blast and shock. Does anyone know how far the Enola Gay dove before leveling out?
 
I recall about 1,500 feet at about 300 mph.

In The Tibbets Story, Paul Tibbets recounts that during preparations for Operation Crossroads (specifically Test Able), a practice bombing run went tragically wrong. A B-29 crew, led by Major Dave Semple, attempted a steep pullout after a simulated drop. The maneuver overstressed the aircraft, tearing the tail section off midair. They all bought the farm.

Tibbets described it as a sobering moment that underscored just how dangerous even the rehearsals were. In tribute, Semple's replacement crew named their aircraft Dave's Dream—the same B-29 that would go on to drop the Able bomb over Bikini Atoll.

Paul Tibbets was quite candid about that in his memoirs. He believed the decision to assign Major Dave Semple and his relatively inexperienced crew to the Able test drop during Operation Crossroads was driven more by politics than merit. According to Tibbets, the 509th had trained extensively for atomic missions and had the experience to handle the high-stakes nature of the test. But instead of using one of his seasoned crews, the assignment went to Semple's team—who, tragically, were killed during a practice run when their B-29 broke apart midair.

Tibbets saw this as a bureaucratic misstep, where command decisions were influenced by internal politics, perhaps to give other units or officers a share of the spotlight in the postwar atomic era. The loss of Semple's crew was a devastating reminder that atomic delivery wasn't just about flying a bomber—it demanded precision, discipline, and deep familiarity with the aircraft's limits.

The Able test of Operation Crossroads in July 1946 was the first postwar atomic bomb test, and the air-dropped bomb missed its intended target by about 2,130 feet (650 meters). The bomb, nicknamed "Gilda", was dropped from the B-29 Dave's Dream and was supposed to detonate directly over a fleet of decommissioned ships anchored at Bikini Atoll. Because of the miss -- The damage to the target fleet was far less than expected -- Only five ships were sunk, and many others survived with limited damage.

Experience matters!
 
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Would doing a Lancaster+ improve the performance sufficiently? Especially altitude performance?
 
I agree. I would studiously ignore Mark Felton's video about the subject, he gets a lot incorrect and doesn't even mention the Thin Man bomb, the only reason the Lanc is mentioned in the Manhattan Project. I wrote a lengthy article about this very subject which was published in the British magazine Aeroplane Monthly five years ago, which goes into detail about the performance differences between the B-29 and the Lancaster, as well as technical details behind the bomb. This is the online page, but it was published in the hard copy mag.


Regarding the in flight refuelling, no RAF aircraft was equipped to undertake in flight refuelling by the end of the war, despite Tiger Force being slated to rely on it. A commencement date for Tiger Force wasn't until early 1946, so IFR was simply not realistic along the timeline of things. We have a thread about the Lancaster atom bomber here on this forum but it became a little heated, so it was shut down. There are some who frequent this site who have put forward totally fantastic figures and concepts beyond what was available at the time as reason why it could have worked, but for the very reasons you state above, Allan, the Lanc couldn't do it. It simply did not have the performance, even with 60 series Merlins, top turrets removed and so on. It's just a non-starter and the atomic raids reflect the sheer capability of the B-29 as a cut above everything else in service at the time, that's why Arnold spent so much energy pushing for it.
 
wuzak said:
Would doing a Lancaster+ improve the performance sufficiently? Especially altitude performance?
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If there was enough effort thrown at the problem it could have been done, but timeliness was the issue. The B-29 is the benchmark, whether we like it or not. If the British were to build a Lancaster that could match the B-29's capabilities the big issue is when would work start on it to be able to do the raids in August 1945. You are essentially starting from scratch because you certainly want the aircraft to be pressurised. It has to have the range to fly from Tinian to Japan and back, possess performance to do this at similar heights as the B-29 and at a reasonable speed. Forget Okinawa as a forward operating base, it has to perform the rendesvous and what have you that the two raids did, from Tinian. And before anyone says that Bockscar landed at Okinawa, it wasn't originally intended that it do so, it was the operational issues that occurred that led to that happening; Okinawa was a diversion site, not the actual destination.

It is a big ask and the airframe/engine combination as it was, was simply not up to the task, which neatly takes us back to a clean sheet design.
 

You're conflating two discussions.

The aim is not for a nuclear bomber to bomb Hiroshima and Nagasaki, but for a high altitude heavy bomber that can carry either the Tallboy/Grand Slam or equivalent weight in conventional bombs.

The aim is to have a higher performance aicraft than the Lancaster, especially in load carrying and altitude performance.

The Lancaster Mk VI, with 2 stage engines, had improved ceiling and top speed, but its ceiling was still only 28-29,000ft.
 
Could they have made a new wing to fit the existing Lancaster fuselage, a "high speed wing"?

It could be a long span wing with 6 tractor engines, but could an alternative with 4 tractor and 2 pusher engines be viable?
 

Not necessarily. The B-29 is still the benchmark. The aircraft has to be pressurised if you want the altitude performance, and then there is the range and payload, which should be able to match the B-29 on the atom bomb missions. It is a big ask, but realistically, there's no choice, otherwise the RAF acquires Washingtons, which defeats the purpose of a new big bomber. Let's face it, you are not really going to want to achieve the altitude performance without a pressurised airframe, so that means the Lancaster airframe is out.
 
Well, yes, it would need to be pressurised.

Wallis' Victory Bomber would have been pressurised, the Windsow was.

It would have been possible, I'm sure, to pressurise the main part of the crew cabin of the Lancaster - the tail gunner and upper turret operator may miss out.

One issue for the Lancaster fuselage was the requirement to carry a Grand Slam. Sure, the Lancaster did, but it did so with the bomb doors removed, bomb bay faired in and the bomb slung under the fuselage.
 
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