The U.S. has agreed to ship back Pac 2 Patriot anti-aircraft missiles Taiwan sent to the United States for upgrades in 2008. These were to have been sent back in 2009 but were delayed for three years by, well, no one will admit exactly what the reason was. Might have had something to do with China pressuring the United States to not send weapons to Taiwan.
Taiwan has been trying to upgrade its Patriot anti-missile systems for a decade, but the U.S. support for this effort has been somewhat half-hearted. Last year Taiwan received its first Configuration-3 radars for its Patriot anti-aircraft missile systems. This upgrade enables Patriot to fire Pac-3 anti-missile missiles. The PAC 3 is smaller than the anti-aircraft version (PAC 2), thus a Patriot launcher can hold sixteen PAC 3 missiles, versus four PAC 2s. A PAC 2 missile weighs about a ton, a PAC 3 weighs about a third of that. The PAC 3 has a shorter range (about 20 kilometers) versus 70 kilometers for the anti-aircraft version.
Three years ago, despite vague Chinese promises that it might remove some of the thousand ballistic missiles aimed at it (which never happened), Taiwan signed a $154 million contract with a U.S. firm to upgrade the island nation's Patriot missile systems. These hardware and software changes will make the Taiwanese Patriot batteries equal in performance to those used by the U.S. Army. That is, the Taiwanese Patriot systems will be able to fire the PAC-3 anti-missile missile and also station the Patriot launchers many kilometers from the system radars. Taiwan has also ordered hundreds of PAC-3 missiles. Meanwhile, China now has 1,600 ballistic missiles aimed at Taiwan.
Increasingly anxious about China's military buildup, Taiwan has been increasing its defense spending. China still spends over five times as much on defense, to support about two million troops. Taiwan has only 350,000 troops and a population of 23 million, compared to 1.3 billion on the mainland. Taiwan's GDP is less than six percent of Chinas. Thus the per capita income of Taiwan is more than three times that of the mainland. Taiwan's military is based on the American model, with an emphasis on quality. China based its military on the Soviet model (where quantity has a quality all its own), although for decades the emphasis was on mobilizing a huge force of guerillas. Now China is trying to develop a force that can fight on Western terms (high tech gear operated by well-trained troops).
While many Taiwanese still see the United States as the ultimate guarantor of Taiwanese independence, they see China as increasingly capable of grabbing the island before the U.S. can intervene. So while the Taiwanese don't have to be strong enough to defeat a Chinese invasion, they do have to be strong enough to hold the Chinese back until American reinforcements can show up.