There have been threads on the Lancaster's ability to drop the Bomb. The Black Lancaster's were trained as a back up for the Bomb delivery. If Germany had developed a Bomb, what aircraft could have delivered a 5000 kg device?
We will assume a 10,000lb 4550kg bomb similar to little boy. As far as I can tell the largest bombs dropped by the Luftwaffe was a SC2500 2500kg (5500lbs) HE bomb. Probably physically as large as a little boy.
Here are the options, only aircraft actually built and used in missions:
1 Heinkel
He 177A5 with either a modified bomb bay or carrying a little boy sized bomb externally with ease. The aircraft had an upper wing layout and there was nothing stopping a modification to allow the large littleboy bomb to be carried fully internally. The B29 itself had to be modified as well. In fact one He 177 was modified with a full length contagious bomb bay that could have carried little boy. This was part of a test program to develop a bomb bay capable of transonic speed release for the
Ju 287 forward swept bomber test bed and its developments the
EF131 and
EF132. During the Baby Blitz raids on Britain in early 1944 the He 177 achieved an attrition rate lower than 6%.
The
He 177A5/R2 reconnaissance version, stripped of much of its armament bar the tail guns could achieve 351mph. Since this would need to be a night attack this configuration with a a tail warning radar and a microwave scanner would make a good basis for penetration into the UK.
2 Junkers
Ju 290A7. This powerful aircraft with 4 x 2000hp engines was well armed with twin 20mm tail guns a powered B24 liberator style turret had also been developed. It evolved from the 1936 Ju 89 bomber so could have had a B17 or He 111 style bomb bay between the wing spars. I'm guessing capable of fitting 4000kg (8800lbs) of bombs but probably nothing much larger than 1000kg/2200lbs. I'm simply guessing on the basis of the B17's 6000lb capacity and the Junkers had a larger wing chord with more room between the spars The Ju 290A7 would have had no problem carry 10,000lbs bomb externally either naked in the slipstream or within a paniers. Although the Ju 290 had been redesigned from bomber to transport role and back again by the time of the Ju 290A5 it had been designed to carry guided weapons such as Hs 293 and Fritz-X externally for its maritime reconnaissance bomber role. A more developed version the Ju290
B with pressurisation and turbo charging for the BMW801 engines was planed. It would have had a very long and large bomb panier capable of carrying a large weapon like a little boy. The rear of the panier served as an excellent ventral gunners station and the front as well. It's BMW801TJ engines were designed for a good high speed cruise at 10,000m-11,0000m (33,000ft) or more.
More interestingly the Ju 290 as a transport retained the C130 Hercules style rear loading ramp or "Trappoklappe" that could be opened in flight. This had come in useful when successful in flight refuelling experiments took place in 1942/43 since the fuel hose reel could be fitted there. (The Luftwaffe used a probe and drogue type arrangement though the fuel was passed up to the receiver) . The "Trappoklpappe" loading ramp had been designed to release parachute supplies and paratroopers but as the Germans had developed high speed drogue ribbon parachutes it might be possible to extract the little boy MOAB style from the rear loading ramp. Loads the Germans had tested with large ribbon parachutes include a Do 335 sized aircraft, Me 163 (to slow these aircraft down for pilot emergency egress, they chose ejection seats instead) and a gliders and Ar 234 jets for quick short landings. The bomb would probably fall at 220ft/sec 70m/sec about what a parachute mine bomb fell at (a parachutist falls at 25ft/sec or 7m/sec.
This also allows about 30-60 extra seconds for the aircraft to escape the atomic blast since the bomb falls slower and also stops its forward motion almost immediately.
A loaded
Ju 290 could operate effectively at speed to over
20,000ft, a little more than a Lancaster, however the planed Ju 290B with its turbocharged BMW801TJ engines about 11,000m
3 Junkers
Ju 390. This aircraft was a
stretch for the
Ju 290 with extra wing span and a pair of extra engines and wing section inserted. This had a remarkable effect on performance.
a/ Speed increased from
278mph to 322mph at just over 20,000ft.
b/ Range doubled to nearly
6500 miles. Enough for a mission from Berlin to New York plus over half way back. Best to New York was 80% of the way back.
c/ wing loading was 60% that of the B29, this gave a remarkable take-off run of less than 500m at MTOW. With 2000hp engines it had a higher power to weight ration than the B29
At 20,500ft the
Ju 390 was not much slower than a B29 (322mph versus 348mph) but if equipped with the turbo charged BMW801TJ the difference would fade to insignificance above 25,000ft as drag of the bigger fuselage became insignificant.
So the Luftwaffe had completely viable options for delivery of a nuclear explosive not only to the UK, USSR (he 177A5) but also the USA (Ju 390). The Ju 390 would require one in flight refuelling in route to its US target to ensure it could fly the return leg but clearly a ditching near a u-boat was a viable option.
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In terms of the German ability to develop an atomic weapon probably by late 1946.
Heisenberg had calculated the critical mass and when asked to explain how big he said it was about the size of a pineapple in 1939 which is about 15-20 kg or Uranium. That is correct. German army ordinance (likely Klaus Diebner) had also estimated 8-20 kg which is closer than the Maude committee to the actual value..
The Germans had several problems in their nuclear program:
1 They had far fewer resources than the allies and cooperation with the Japanese was difficult.
2. They were being bombed, this destroyed no less than 3 of their uranium centrifuges on 3 occasions.
3. They had gained control of Norway's Hydroelectric electrolysis system which was used to manufacture ammonia using electrolysis (fertiliser, explosives, chemicals). Electrolytic cells tend to concentrate the heavier deuteron molecules. This was both a blessing and curse as the head of German Army Ordinance, Schumann, having control of a 'free' source of heavy water declined to invest in the industrlisation of alternative methods such as fractional distillation using waste heat (which was done in Canada). There was a fear that the columns would be attacked. They did develop the
Geib–Spevack (GS) process and orders were placed but it was too late. Espionage and bombing constrained German heavy water supplies even though they knew they could produce a self sustaining reactor.
4. The original German civilian uranium association (made up of interested parties) had made much progress and had great insights into nuclear reactors, moderators, control etc but was displaced when the German military became involved and side lined the association with its own group known as the second uranium association. One of the results was that when the Germans had tried graphite as a moderator and found it wanting a Physicist called both had identified the contaminants and suggested how it should be removed. That message never got to Heisenberg. Hence the Germans remained dependant on heavy water as a moderator from Norwegian sources.
5 When Armaments minister Albert Speer approached Heisenberg and von Weissacker if a bomb could be built in time to influence the war. Heisenberg said no. He was right as the US weapon was only ready and tested 6 months after the European war was over. Had Heisenberg said "maybe but its 50:50" Speer would have supplied Reichs Mark 500 million instead of 46 million. Several others physicists such as Deibner would have said yes. That money certainty would have solved the heavy water problem.
6 The Germans had a number of achievements. apart from discovering Uranium's fissionable properties by 1942 their
"Leipzig Spheres" were the first subcritical rectors to produce more neutrons (5:10 times) than they consumed. These were concentric hollow spheres of uranium with heavy water in between and a radium/boron neutron source in the centre. A scaling to about 2.5m diameter would have been critical as calculated by Klara Doppel.
7 They did manage to enrich Uranium by uranium centrifuge (producing about 2.5 grams enriched to 6%) and some more by a a device known as a uranium sluice.
8 In the closing stages of the war they did have a subcritical lattice reactor at Haigerloch that tested as planned and proved that an upscaling of only 50% would have produced a critical reactor. (there was insufficient heavy water to do this. The core of the reactor is little bigger than a 200L drum.)
After the war Heisenberg was interred at Farm Hall in Britain. Here in 'dinner table discussions' that were bugged he calculated critical mass at about 100kg (way more than his pineapple claim in 1940) which would produce a 20 ton weapon but did say this was without temper (neutron reflector) when he heard of the Hiroshima bomb he quickly corrected himself.
It should be noted that after the war if you wanted to work in academia or the public service in Germany you had to have a certificate of being denazified. Heisenberg was one of the ways one of the people who was needed to grant this in science so unfortunately many German physicists had to shut up, agree with Heisenberg in order to be able to work. It's clear that Diebner, Hatek etc wanted to build a bomb. Heisenberg reduced their effort to a research program to produce a reactor.
There were perhaps 2-3 other options. The He 177
B was a He 177
A with 4 independent
DB603 engines borrowed from the
He 219. It worked very well though its power was a little too much for the tail fin area and range was no better than the
He 177A. It could have been produced but it was decided to develop the
He 277 instead as it would have the range needed to attack allied shipping. It was a fuselage stretch with an enlarged wing, new cockpit, separate engines. There was also the
He 274 (which flew) and the
Ju 488 (which almost flew). The Ju 488 had a service ceiling of
48500ft with
BMW801TJ engines so it would have been beyond allied interception and safe from any atomic blast.
