The following information is widely available in back issues of any SWAT type magazine or even by searching Google so I am not giving away any state secrets or information that might harm a police officer.
Basically, there are two styles of SWAT tactics. East coast (NYPD ESU) and West coast (LAPD SWAT).
East coast SWAT revolves around the ballastic shield and their units religously train with their shields. These East coast units usually wear a lot of heavy armor with groin projectors, shoulder protectors, etc. These are the modern day Spartans. These teams are usually slow and not so dynamic. There is more of a centralized command and control.
West coast SWAT revolves around more of a military thinking. Have you ever see any soldiers or Marines fight on the battlefield with a ballasstic shield? Nope. These west coast teams use their weapons for cover. West coast units are structured in the same way as an Infantry platoon is structured. In an Infantry platoon. I.E. A platoon is seperated into 3-4 squads of 10 men and then each squad is broken up into 2 fine teams. Each team is lead by Sgt. Each squad is lead by a SSgt. Less centralized leadership when compared to east coast. West coast units usually do not wear as much armor or even helmets favoring to be lighter and faster just as special forces units are in the military. The LAPD SWAT just wears a simple bulletproof tactical jacket without a groin, armpit or shoulder protectors.
If you have ever lead a platoon of soldiers in an Infantry company, then you would know that the manual states that your fighting load should never be more then 30% of your body weight. Your combat load should never exceed 45% of your body weight. Back in the day, soldiers were a little bit lighter and more in shape then they are now. The recommended load back then was about 45 pounds when fighting.
Whats going on in Iraq right now and the past few years has been a media event...politicians exagerate the need and use of body armor. During the American Civil War, there was body armor available. During World War I, there was body armor available. In fact, there was body armor available during every war. However, the armor available then was found to be too cumbersome and slowed down the soldier. The armor available during World War I weighed about 40 lbs and was found to be impractical. Amazingly enough today's soldier's armor weighs about 40 lbs and is found to be very practical. Hmmmmm...
During the jump into Panama, soldiers carried over 100 lbs of load and what was seen during that jump was comical. You had young athletic soldiers moving like human turtles. Its lucky that the fighting was not too fierce on those days.
My experience is that the intelligence of leadership declines with every lb an operator has to carry.
Sorry if I went off on a tangent, but there is a lot to write about body armor.
My opinion favors west coast tactics where minimal armor and shielding is used. Instead, the weapon is used to shield the operator vs. a large tactical shield which makes for a larger (slower) target.
Here is an interesting article on combat load by the way...
http://www.globalsecurity.org/military/library/report/1985/IDC.htm