I answered this statement by Pope Francis a while back on /r/badhistory. I will repeat that answer below. I address the difficulties of attacking rail lines specifically. I hope the slightly irreverent tone of my post will not take away from its content now that it has been transplanted into this forum.

To address your other questions, the Vatican had some knowledge of the reality of the camps, but it was fragmentary and contradicted by other reports. The Vatican opposed aerial bombardment of civilians (castigating the practice dating back to WWI and making several unsuccessful appeals to FDR on the subject), but never issued a statement regarding bombing the camps themselves. As for the Allies doing more, Normandy and Market Garden were already risky moves in the West, and the Soviets were in for a massive fight. Without drastic changes to how the war was fought it was ended as soon as possible--and making those changes takes us into "what if" territory (forbidden on this sub).

So, Pope Francis did an interview with "La Vanguardia" recently. The full text in English is available here. During the interview the subject of Pius XII during WWII was brought up. I'll have more on that further down, but the offending bad history text is quoted below:

Did you know that they knew the rail network of the Nazis perfectly well to take the Jews to concentration camps? They had the pictures. But they did not bomb those railroad tracks. Why? It would be best if we spoke a bit about everything.

Well, papa, I am a Catholic. I love the Church, and I take my faith seriously. I'm a student of papal history and of WWII, especially military aviation. I take all of that seriously. You're not the first to ask why the rail lines to the death camps weren't bombed, and you won't be the last. It seems like a great solution--just keep the Jews from being delivered to the camps!

Sadly, it wasn't that easy or simple.

Even if we disregard the immense cost of bombing operations (both in terms of economic cost and that of human lives) and the difficulties of targeting something even further east than most of the bombers' normal targets (which were already near the limits of their endurance), we would still have a major issue to deal with if we determine that attacking the rail lines leading to death camps is important enough to divert the bombers from their other targets. Further, any kind of precision bombing had to be done in daylight. That was murderously expensive at best prior to 1944, with first the British then the Americans learning the harsh lesson that bombers without fighter escorts could not sustainably bomb targets in Germany during daylight. And by "sustainably" I mean that bombers and crews were being lost at such a rate that the force would be destroyed in a handful of missions. Only after long-range fighter escorts were created in 1944 were the bombers able to keep up a daylight offensive for any length of time. So, only in 1944 and 1945 would such a sustained campaign against rail lines leading to death camps even be possible. But that's not even the issue.

The issue is this: WWII bombers were largely ineffective against rail lines.

There are a number of reasons for this. The first is that WWII bombers were not accurate enough to reliably hit a rail line. Keep in mind the very nature of a set of rails--they are a ribbon of infrastructure mere feet wide that snakes through the country. Now we add the difficulties of WWII bombing that resulted in most bombs ending up nowhere near their intended target. Specific factories were often missed by the bombers tasked to destroy them, and there were many times in which entire cities were missed by the bombers. The 'solution' to this difficulty was to send more bombers (again, at great expense) so that you could drop more bombs in the hope that one of those bombs would hit its target. This was somewhat effective.

There were operations undertaken against German rail lines. Most prominently, they were targeted as part of the 'Transportation Plan' prior to D-Day. As reconnaissance during the war indicated and surveys after the war confirmed, there was some success for a time. Rail lines, if targeted with large numbers of bombers, could be disrupted--but only for a short time. But unless a bridge or viaduct was somehow heavily damaged or destroyed (something only 'tallboy' and 'grand slam' bombs very late in the war had any real chance of accomplishing), the railroad would be repaired in short order. Basically, most of the time the trains were able to roll through the targeted area in 24 hours. This is partly due to the aforementioned difficulties in targeting rail lines, but the Germans also had dedicated forces to repairing railroad damage. In addition, these units would compel local people to assist in the reconstruction of the rail line. Further, outside of bridges and viaducts railroads are basically piles of rocks and gravel with a little wood and steel beams on top. This means that low-tech solutions were perfectly suitable to fixing the damage caused by relatively high-tech instruments such as heavy four engine bombers equipped with every modern piece of equipment. German railways only collapsed extremely late in the war, basically when every other service had also shut down and the government had effectively collapsed.

In the final analysis, rail lines could only be cut on a tactical basis. Within a matter of hours repairs on a damaged line could be completed, so to ensure that a rail line was not used it would have to be retargeted multiple times. This meant that the bombers could not be used to attack other targets that were also deemed worthy of their attention. So, to target the railways leading to the death camps, bombers would have to undergo great risks (at great expense both in money and men) repeatedly (because the Germans had great success in repairing rail lines within hours) to even have a chance at success, and other targets would have to be neglected. So, even had Allied command known every detail of the horrors of the camps, it would have had to be an immense undertaking to try to interdict travel to those camps.

So, papa, the Allies couldn't have bombed the rail lines leading to the camps. Not really. They would have had to dedicate a huge proportion of their bomber force to accomplish the task, the costs would have been very high, and forced laborers with nothing more complex than a shovel could have repaired the damage in less than a day making it necessary to repeat the dangerous operation all over again the next day. Using low-level attacks by smaller bombers would have been impossible because those bombers didn't have the range to get the job done (and would have had smaller bomb loads anyway). Even isolating the Normandy battlefield was a huge stretch for the Allied bombing force, and they still chafed at being used in such a role instead of attacking German industry.

It sounds like a great solution, but the realities of bombing in WWII didn't allow for simply isolating the death camps by cutting their rail lines. Even then, we would have had no guarantees that the Germans wouldn't have simply found another way of carrying out their murderous policies--in the same way that they found a way to increase wartime production during 1944-45 despite the increasingly devastating attacks of the same bombers in question.

Sources:

Christian Wollmar, Engines at War

Martin Van Creveld, Age of Airpower

Walter J. Boyne, Clash of Wings

Robert Leckie, Delivered from Evil

As always, followup questions from OP and others are encouraged!

This exact issue is fantastically covered in this badhistory post by /u/Domini_canes, although he specifically covers the Pope's idea that they might have bomber the railway lines. In essence bombing the railway lines was not feasible as WWII bombers were not effective against rail lines. I encourage you to read the entire post as it's really fantastic.

As for speeding up the landings I'm afraid I can't comment with any degree of expertise or provide further links. Hopefully another flair who can will pop up.

The Allies could have done more, but not really in 1943. Up until 1941 they could have done some things that would have helped.

• Increased limits on Jewish immigration before the war.
• Allowed food aid to be delivered to occupied countries.

Now these would have helped, and this is where I wish my country had done more. But I don't think that even this would have prevented the holocaust entirely. There are huge logistical hurdles with both ideas when you try to scale them up. Feeding or relocating 6-12 million people is no easy task. The Nazi officials found it easier just to murder an entire race than to try and feed, clothe, and house them.

That I think leads to the second point. Many of the people who died where shot, drowned, gassed, or blown up right where they lived. This is especially true of communities in Ukraine or Russia. I am very doubtful that just preventing people from being transported to death camps would have saved that many lives. Not only did they have mobile killing units, but blowing up train tracks would not have made the food situation any better.

So there were certainly things that the Allies could have done, but a military solution (other than the defeat of the Nazi party) was probably not one of them.

Simply yes, they knew about the holocaust, although not the extent it was going on. The year before the war broke out around 10,000 (mainly) Jewish children were accepted into the UK under the scheme known as 'Kindertransport' so before WWII Britain at least were not under the ruse that human rights for the Jewish community in Germany were not being violated. The scheme was actually set up following Kristallnacht which was documented in British media so the UK knew about the rising violence in Nazi Germany. https://en.m.wikipedia.org/wiki/Kindertransport

The British public knew about the Holocaust and concentration camps around 1942 when it started to be documented in British media. However, Churchill condemned it as early on at Nov 1941;

''None has suffered more cruelly than the Jew the unspeakable evils wrought upon the bodies and spirits of men by Hitler and his vile regime. The Jew bore the brunt of the Nazi's first onslaught upon the citadels of freedom and human dignity. He has borne and continued to bear a burden that might have seen beyond endurance. ''

Churchill himself actually tried to do quite a lot about the Holocaust, I know this is just a BBC revision website but it's got some pretty useful information; http://www.bbc.co.uk/history/worldwars/genocide/churchill_holocaust_01.shtml

But in short, the British did not do a lot to stop the Holocaust purely because there was not a lot that could of been done. The accuracy of the fighter planes were nothing like the ones we have today and bombing of the concentration camps would have more than likely resulted in more deaths than saviours, that's after the planes have managed to locate and fly that far on small petrol tanks. The British also had their own country to worry about that was being destroyed by the Blitz and I doubt the generals could have justified sending out troops to save people when it would more than likely have led to more casualties.

(Sorry about any format I'm on mobile and please add to this as I'm sure there is a lot more evidence and argument I'm just going off the top of my head with a couple sources to support it.)

Edith Stein, gone but not forgotten.

Related question: Everyone here is focusing on direct military actions, but I recall there were active efforts to get Jews out of Europe during the war that ran into a lot of obstacles. Some countries (especially the Arab countries) actively tried to impede these efforts, while most other countries simply didn't help. Is my impression accurate? Could the allies have done more to facilitate those efforts to help get Jews out, and also to give them places to go to?

The Germans had little difficulty killing Jews (and others) before they built the Extermination Camps. Before the camps they had roaming execution squads who just rounded up Jews where they lived, marched them off into say a nearby forest, had them stand at the edge of a pit and shot them in the back of the head.

The extermination camps weren't chosen because they were the only way to kill Jews, obviously, or because it was quicker, but because it was easier on those carrying it out. There were all sorts of psychological issues with shooting large numbers of people. Camps also had problems. You had to transport the people to them which as you can imagine wasn't as quick as just shooting them near where they lived. It also had the problem of body disposal since the camps couldn't just be moved to another location. I don't think I've ever seen any historian claim that the camps sped up the Holocaust due to all the difficulties the camps entailed.

I doubt the Germans would just have given up the Final Solution if the train tracks, etc to the camps were bombed. They had already killed a huge amount by other methods.

Hey, what about the Evian Conference? https://en.wikipedia.org/wiki/%C3%89vian_Conference

I read that Hitler was in favor of letting the Jewish population leave to other countries, but the US and GB didn't really act on the promise of the conference, leading the other 30 or so countries to follow their lead. After that conference surged the "final solution to the Jewish problem".

Please enlighten me if wrong.

Yeah, the Allies did nothing except give up thousands of their lives to defeat the Germans. This guy has literally made a career out of being wrong.