In 2005 Boeing Satellite Systems, Inc. (BSS), began production of the 11th in a series of UHF Follow-On (UFO) satellites for the U.S. Navy. The Navy began replacing and upgrading its ultra-high frequency (UHF) satellite communications network during the 1990s with a constellation of Boeing 601 spacecraft known as the UFO series. The agreement to build F-11 amended an existing 1.9 billion contract under which BSS built and launched 10 UFO satellites. With this authorization to proceed with F-11bs construction, the Navy moved to sustain the UFO constellation into the latter part of this decade.