The Brits got some U-2's very early................... but they were probably on lease
I'd suspect the US will lease 2 older Virginias (which al least you know are worked up and have the bugs rung out) and add a couple to their run. The Astutes are coming of a single, very slow line that is needed for other things by the RN. Remember they are building a class of 7 boats - the first one was laid down over 20 years ago and they are still building the last two.