Operation Blue Sky was a UNIT operation. It took place in London in the year 2009. It was a raid on the London headquarters of the company ATMOS to discover whether the company was harbouring illegal aliens.
Operation Blue Sky was coordinated by Dr. Martha Jones. It ended in them taking over the company's factory and using it as a base. The ATMOS staff didn't attack or resist arrest. (TV: The Sontaran Stratagem)
With several days of planning, Martha positioned UNIT soldiers in preparation to invade the factor on her command due to suspicions that the staff were doing things with ties to alien origin. Before ordering the attack, Martha contacted the Tenth Doctor, briefly reuniting with him and his new companion Donna Noble. She then used her radio to order the assault, something that caused Donna to remark that the Doctor had turned Martha into a soldier
After the initial attack was a success, the UNIT team took the staff as prisoners while they searched the area. While the Doctor was taken by Martha to meet UNIT's head of the operation, Donna went to the paper work for the staff finding such empty. She came back with one of the empty files to show the Doctor and Martha, remarking that surpsorongly not one staff member had taken a day off of work. Such caused Martha to investigate by doing medical tests on the staff members, finding one person's heart rate was extremely high despite their placid nature. (TV: The Sontaran Stratagem)