user: Question: What is the yield in NTS Area U2r when the purpose is Weapons development?
Columns: ['Name', 'Location', 'Elevation + Height', 'Delivery', 'Purpose', 'Yield']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Izzer', 'NTS Area U9bp', 'metres (ft) - metres (ft)', 'Underground shaft', 'Weapons development', 'less than 20 kt']
SQL:

assistant: SELECT "Yield" FROM "Table" WHERE "Purpose" = 'Weapons development' AND "Location" = 'NTS Area U2r';