The PLA (People's Liberation Army, what the Chinese call their armed forces) has several branches with air defense responsibilities. These include two (air force or, PLAAF, and naval air force, or  PLANAF) which operate fighter planes and three (PLAAF, air force,  PLAGF, ground forces and navy, or  PLAN) which operate both SAMs (Surface to Air Missile) and gun type AAA (anti-aircraft artillery) weapons. Historically, long range SAMs were organized as a separate branch or service (until incorporated into the PLAAF in the 1950s). There is an integrated national air defense system which, to some extent, is a joint organization theoretically capable of using, for example, PLAN fighters in defense of targets in China. 

This system has been substantially untested since the Viet Nam era, when it did successfully detect and engage US aircraft straying into Chinese airspace. It may have been tested during operations against Viet Nam in 1978. But apparently the airspace over that battlefield was uncontested by either side at that time. China suffered from having no bases in range. Vietnam had bases but either did not fly, for fear of Chinese air defenses, or it tried and failed to penetrate.

The focus of Chinese air defenses is the point defense of vital targets, both of a military nature, and in the sense of major concentrations of civil assets, especially in major urban areas. It is this focus which is the root cause of so many branches of air defense organizations. The Army Ground Forces, the Navy, and the Air Force all operate point defense units at vital bases and with high value mobile units (including all armored formations and warships). These point defenses are autonomous, and can be expected to attempt to function, regardless of the effectiveness of the (PLAAF run) national air defense system. And that national system itself, while using weapons with longer ranges than true point defenses, is focused primarily on defending the approaches to high value target areas. In that sense, it also may be regarded as a form of point defense. While the possibility of true area defense operations is not technically impossible to long range fighter units of the PLAAF (especially J-11/Su-27/Su-30 aircraft) it is not expected that the aircraft will often be employed in this way. 

The PLA was disturbed by the ease with which US forces defeated Iraq in 1991. One conclusion they reached was that the US freedom to operate at will in the air was an essential element of the US success. In the 1990s, China encouraged contractors to equip and advise Iraqi air defenses. From this vantage point they observed US operations in 2003, no doubt recording electronic signals for analysis. It also appears they succeeded in making forward helicopter operations excessively expensive, to the point that many American operations were not attempted. Based on observations in both the 1991 and the 2003 campaigns, the Chinese have attempted to devise more effective air defenses. They have upgraded to more advanced missile systems, notably TOR-M1 and S-300 from Russia, as well as developing a variety of gun and missile systems domestically. While these systems are often criticized as junk in the west, it appears that China has a robust and effective industry which is being used, in a competitive environment, to field better systems. It is likely that some, if not most, of these new systems will be effective. The technologies are being applied comprehensively, from a new AAA type .50 cal (12.7mm) machine gun (designed to replace the 14.5mm weapons on many AFVs and small craft) to ABM (anti-ballistic missiles) capable variants of longer range SAMs. Each weapon is provided with three or four different kinds of sensors to insure that effective countermeasures are hard to achieve. They have not accepted foreign standards for radar or missile performance, and constantly are devising modified or alternate systems to improve them. This often slows down development, sometimes by years. But the end result is usually at least marginally better than competitive systems in other countries. The sheer numbers of systems, and the number of ways they can obtain target information, is large enough to make approaching vital points in China problematical, and likely to involve attrition. -- Sid Trevethan