The Arab world's nations are packed with Soviet SAMs bought in response to Israel's air superiority and designed back in the 60s and 70s with the B52 in mind. Not to mention Patriots in Israel and Saudi Arabia, and a number off high-altitude interceptors in the air forces of those countries. If the US send out a message to Turkey, Syria, Lebanon, Egypt, Israel, Saudi-Arabia, Kuwait (and their own forces in the region which, right now, are considerable), I don't think a rogue B52 has a chance of getting through. Even under cover of US fighter squardonas, they don't let them operate over enemy territory much any more. They use cruise missiles as standoff weapons.
However, I think the idea of a Christian Fundamentalist group nuking Mecca is just disturbingly plausible enough. A suitcase nuke could be smuggled in, or a private aircraft used. It would be challenging, though.
- To my knowledge there has as yet been no proven case of weapons-grade fissile material destined for terrorist hands. There have been cases of interception of materioals going into dubious channels, and some material has disappeared, but those were, AFAIR, destined for nation states, not terrorists. If I were a Russian mafioso, or just a colonel inthe Strategic Rocket Forces with a lousy retirement package, I might consider selling a warhead to Saddam Hussein or a few pounds of Plutonium to Kim Jong Il. After all, they just want to have it. But terrorists want to use it - the risk to all involved is much higher. think of the pressurebrought to bear to find the perpetrators after 9-11 and multiply. Al Qaida wouldn't get as much as a phosphorescent watch from me
- Saudi Security is probably not as good as it would like to think, but it is better than its record with Islamic terrorism suggests. A Christian group can not count on sympathisers, even of the 'I don't really want to know' variety. Either they are very good indeed, or they find a method of delivery that does not require any actual preparatory work in the country.
- Methods of delivery do not include just flying it in. THe sky over the Middle East is fairly thoroughly watched. Back in the late 80s, a MiG pilot ejected over East Germany and his leaderless, damaged plane made it all the way to Holland. Even at such short notice (less than 45 minutes for the whole business), the air defenses noticed it from the second it crossed into West German airspace and tracked it all the way to its impact. I would think Saudi Arabia to be a lot more trigger-happy where unidentified aircraft are concerned.
- During the Hajj, it is easy to get to Mecca IF you are a Muslim (if you are not, you need the kind of special permit that only really senior people can obtain for you). Could they set up someone with a convincing Muslim identity? I think it would be possible, but again, not easy. Especially given the kind of interest Western services take in converts these days.
My scenario: A group of anti-Muslim terrorists con a Russian seller into thinking they represent a rogue nation (say Myanmar) intersted in obtaining fissile material. They manage to smuggle it to Western Europe and there assemble a simple nuclear device and a timed trigger. That way, they evade the unpredictable checks at US ports and, with luck, the more relaxed controls at the German-Polish border. Still, this is the most high-risk aspect of the business. They then set up a trading company as a front, delivering machine tools or other technical goods to the Middle East. This will take a good deal of capital, but should not be too hard. They then need to secure a contract that will result in a consignment being delivered to Mecca during the Hajj. THe container is loaded with the bomb and filled up with genuine merchandise and sent out by sea, legit, through Rotterdam or Hamburg (not a smaller port - volume means security). Timed to explode on a certain day, all you need to do now is trust in the punctuiality of your delivery company.
Much more scarily, this method of delivery should also work for places like Liverpool, London, Hamburg, Rotterdam, Singapore, Hong Kong, New York or San Francisco.