UNIT base, Washington
From Tardis Wiki, the free Doctor Who reference
UNIT had established a base in Washington by September following the Planetary Relocation Incident, when the 456 took control of every child on Earth. UNIT ran tests on a couple of children including brain scans, blood sugar and a check for radiation. At Torchwood Cardiff, Captain Jack Harkness received a call from who he called "Sergeant Grunt", who informed him that UNIT had found nothing from the tests. (TV: Children of Earth: Day One)
