Zephyr was built by controversial UK defence boffinry selloff bonanza company Qinetiq. It's intended for development into a military platform able to cruise above a battlefield or other area of interest for weeks or months on end, providing such services as surveillance or communications relay. A Qinetiq spokesperson informs that "the Zephyr set down successfully at the US Army's Yuma Proving Ground in Arizona at 15:04 UK time this afternoon, having been airborne for no less than 14 days and 24 minutes."
During the night the Zephyr runs on lithium-sulphur batteries, which're recharged during the day by its solar cells. Qinetiq says that the machine carried a "a communications payload configured to meet the needs of UK Ministry of Defence" during its record-breaking flight. The Zephyr has now well and truly busted the official world record for the longest flight for an unmanned air system (set at 30 hours 24 minutes by Northrop Grumman's RQ-4A Global Hawk in 2001).