You could easily get it on the annual bid at SKW. Basically you can bid as much vacation as you like, and three consecutive weeks should be doable if you don't overlap high-seniority holidays...but when the date arrives, it's up to you to ensure you have enough combined vacation time and personal time to pay for it. You would probably have to be at the two year point to have accumulated that much vacation (and not have called in sick a lot).

Actually this is the way I prefer to do it. I just bid days off for most events in the US, and then every couple of years I take a big chunk of actual vacation and go overseas.