Despite representations to the contrary on several postings on this thread the 2 'tanks' slung under the wings on a U-2 are not for holding fuel. They are called superpods and generally contain lots of SIGINT sensors however they are optional depending on the sensor payload of the mission aircraft. Some U-2 missions are/were flown with a slick wing configuration.
It's a great aircraft. I had the pleasure of working on sensor and datalink systems on them (based out of RAF Alconbury) from 1990 to 1994 when they left Alconbury. I had a great time and worked with some real characters many of whom had been with the programme for many, many years and who had fantastic stories to tell.
One of my former colleagues (a civilian contractor) left Alconbury to go to an island somewhere in the med that is/was known as Det 3 in the U-2 world
. When I later went there on holiday I contacted him and we spent a very enjoyable evening out in town - Brandy Sours all around.