Unless your destination is actually the US, you don't need a US visa. If you have to divert to a US airport for some reason and you do not have a US visa, well that is force majeure and they will just have to accommodate you whilst you need to stay. It is not a problem, but the Immigration Service will probably try and make it one. You do not need a Crew US visa if you are flying to Brazil. You will not ever divert to the US on this route from Europe!
When you have to get a US Visa, an awful day trip to the US Embassy in London and long queueing for the 1 minute interview is needed. If you have all your paperwork and you go somewhere abroad where a US Embassy is accessible, it is often far, far easier to get your Visa there, without queueing, quite easily.
They don't tell you that.