It’s usually the missile that gets all the the attention. The deadly rocket that screams through the sky to take out another missile, sometimes traveling far faster than the speed of sound, in what’s often likened to a bullet hitting a bullet.

But perhaps the most important part of the Patriot missile system isn’t the missile. It’s the radar.

That’s the part that first detects the incoming threat. Sometimes it’s an enemy plane, or a drone. Sometimes it’s another missile moving at a mile a second, which makes every second count. The more time to counterattack, the safer you are.

Raytheon, which makes the Patriot, recently announced a significant upgrade to the radar, which the company says will allow it to have a 360-degree view of the battlefield and also see them at greater distances. The company has invested $150 million over the past 15 years in the technology, it said.

“The radar is the key to the system,” said Norm Cantin, who oversees the upgrade effort at Raytheon. “It’s the eyes, and it has to be able to see far enough to give the missile time to hit the target. You don’t want it to take the threat out right above your head.”

Development of the Patriot surface-to-air missile system dates to the late 1960s, when it was designed to protect Europe from an air assault by the Soviet Union. While originally intended to take out enemy aircraft, it was upgraded in the 1980s to defend against other missiles.

Patriot became something of a household name during the Persian Gulf War, when the systems thwarted incoming SCUD missiles, launched from Iraq. (Though there has been some debate about Patriot’s effectiveness during the conflict, Raytheon has vigorously defended its performance.)

The Patriot system has continually gone through upgrades since then, and was used again at the beginning of the Iraq War. In addition to the U.S., the system is used by 12 other countries, including Germany, Japan, Israel, Saudi Arabia, Kuwait, Taiwan, Spain, Korea and the United Arab Emirates.

On Thursday, Raytheon announced that the U.S. government authorized it to sell its radar sensor upgrade, called the Active Electronically Scanned Array, to foreign partners. But it’s not yet clear whether they will be installed in the systems now in use by the U.S. military.

The Pentagon is holding a competition for the radar upgrades. A contract isn’t expected to be awarded until 2017.

This post is part of an ongoing series examining the weapons and defense systems purchased by the U.S. government. For previous entries, read about the Pentagon’s electromagnetic rail gun, and the laser weapon that deployed aboard a Navy Ship in the Persian Gulf.