Bermuda
In May 1940, the US requested base rights in Bermuda from the United Kingdom, but British Prime Minister Winston Churchill was initially unwilling to accede to the American request without getting something in return. In September 1940, as part of the Destroyers for Bases Agreement, the UK granted the US base rights in Bermuda. Bermuda and Newfoundland were not originally included in the agreement, but both were added to it, with no war material received by the UK in exchange. One of the terms of the agreement was that the airfield the US Army built would be used jointly by the US and the UK (which it was for the duration of the war, with RAF Transport Command relocating there from Darrell's Island in 1943).

Q: What was one thing the UK wanted in return for granting access to Bermuda?
the airfield the US Army built would be used jointly by the US and the UK