full-scale, operational uncrewed aircraft UAVs by flying for 33.1 hours at altitudes up to 60,000 feet over Edwards AFB. From its first flight in 1998 to 9 September 2013, the combined Global Hawk fleet flew 100,000 hours. 88 percent of flights were conducted by USAF RQ-4s, while the remaining hours were flown by NASA Global Hawks, the EuroHawk, the Navy BAMS demonstrator, and the MQ-4C Triton. Approximately 75 percent of flights were in combat zones; RQ-4s flew in operations over Afghanistan, Iraq, and Libya; and supported disaster response efforts in Haiti, Japan, and California. From 10 to 16 September 2014, the RQ-4 fleet flew a total of 781 hours, the most hours flown by the type during a single week. 87 percent of flights were made by USAF RQ-4s, with the rest flown by the Navy BAMS-D and NASA hurricane research aircraft. The longest Global Hawk combat sortie lasted 32.5 hours. Downing by Iran On 19 June 2019, a U.S. Navy BAMS-D RQ-4A from NAS Patuxent River flying over the Persian Gulf near the Strait of Hormuz was shot down by a 3rd Khordad surface-to-air missile fired from near Garuk, Iran. Iranian Foreign Minister Javad Zarif said that the drone had been in Iranian airspace, while the United States maintained that the drone was in international airspace 18 nautical miles (34 km) away from Iran. NASA In December 2007, two Global Hawks were transferred from the USAF to NASA's Dryden Flight Research Center at Edwards AFB. Initial research activities beginning in the second quarter of 2009 supported NASA's high-altitude, long-duration Earth science missions. The two Global Hawks were the first and sixth aircraft built under the original DARPA Advanced Concept Technology Demonstration program, and were made available to NASA when the Air Force had no further need for them. Northrop Grumman is an operational partner with NASA and will use the aircraft to demonstrate new technologies and to develop new markets for the aircraft, including possible civilian uses. It was reported in the March 2010 issue of Scientific American that NASA's Global Hawks were to begin scientific missions that month, and had been undergoing tests in late 2009. Initial science applications included measurements of the ozone layer and cross-Pacific transport of air pollutants and aerosols. The author of the Scientific American article speculates that it could be used for Antarctic exploration while being based in Chile. In August–September 2010, one