Going to War - GPS Declassified: From Smart Bombs to Smartphones - page 116

wheeled vehicle or helicopter. 60 The slgr weighed three and a third pounds
and was about two inches thick by seven inches square—small enough and
light enough to hold in one hand. With the switch of a button it could display
coordinates in several different mapping grid systems, making it usable for
aviation, ground movements, and artillery support. 61 The difference in cost
between the slgr and Manpack exceeded their size and weight differences.
A slgr cost about $3,400, whereas the Manpacks cost $45,000 apiece. 62 The
Magellan nav 1000, smaller still and battery-powered, was the second most
popular receiver, with about one thousand used in the Persian Gulf War. 63
Commercial receivers provided accuracy to within about eighty-two feet in
each direction (latitude, longitude, and altitude) compared to the ifty-three-
foot accuracy of military receivers. 64 The military later developed a receiver
known as the plgr (precision lightweight gps receiver), which decoded the
encrypted signal and was resistant to jamming (radio interference that blocks
the gps signals) or spoofing (false signals broadcast to cause receivers to gen-
erate incorrect coordinates).
Soon after the first troops arrived in Saudi Arabia, the Pentagon began plac-
ing orders for commercial receivers and eventually ordered about ten thou-
sand. Some service members asked their families to ship them commercial
units. The demand strained production capacity, and by the war's end, the
number deployed by all branches of the military totaled 4,490 commercial
and 842 military receivers, with the Army absorbing about four-ifths of the
commercial versions and two-thirds of the military ones. 65 Coalition partners
began the conflict with about two dozen receivers and eventually fielded more
than two thousand of the devices, which Arab ground commanders dubbed
“the magic compass.” 66 As with aircraft, U.S. ground commanders apportioned
available receivers where they thought they could do the most good. This meant,
for example, divvying up three thousand receivers among forty thousand vehi-
cles in the VII Corps alone. Receivers typically went to reconnaissance teams,
artillery surveyors, and the forward units leading the charge. 67
Recognizing immediately that gps would be vital and most receivers could
not use the encrypted military signal, the Pentagon on August 10, 1990— eight
days after Iraq invaded Kuwait—disabled Selective Availability, the intentional
degrading of the civilian signal to make it less accurate. The U.S. Air Force
Space Command, which manages the satellites and ground control stations,
had first activated the security feature only five months earlier, on March 25.
Commanders reasoned that Iraq lacked weapons that could use gps. However,