The U.S. Army plans to keep its M-2 (Bradley) IFV (Infantry Fighting Vehicle) for another twenty years. To do that, it wants to upgrade thousands of them to "Block II" status. There are already 600 "Block 1.5" (BUSK) upgrades. These are the M-2s modified for urban warfare, based on Iraq experience.
The M-2 BUSK (Bradley Urban Survival Kit) upgrades were applied in two batches over the last few years (the program ended in 2008). The first included a more powerful (at 3 million candlepower, four times brighter) spotlight. There was also a wire mesh protector to keep the optics from getting scratched, and non-conductive rods that push away fallen electrical wires that often endanger crews. Later came a remote control (CLAW) 5.56mm machine-gun on the turret, additional armor underneath to provide protection from mines and a bullet proof, and a transparent shield for the commander when his head and shoulders are out of the turret.
Some non-urban warfare improvements were also made, including a series of sensors and a software package that more quickly found components that were wearing out (so replacements could be ordered and installed), and simulation software so the gunner could train (with the fire control system, in effect, turned into a realistic video game.) All this added about three tons to the weight of the vehicle, making the M2 a 30 ton vehicle (about what most World War II tanks weighed).
The Block 2 is planned as a major upgrade of the M-2. It will include a more powerful (800 versus 600 horsepower) engine, a more powerful gun (30 or 40mm) and lighter armor (or protection systems that shoot down anti-tank missiles and RPGs). Improved sensors are planned, plus vidcams to give people inside the vehicle a 360 degree view of what's outside.) More electronics, including one that would allow variable power, and fuel consumption, from the engine. More safety features are planned as well, including an improved fire extinguisher system. For better protection against mines and roadside bombs, the body of the vehicle would be 18 (46 cm) inches off the ground, instead of the current 11. With more armor on the floor, and seats that absorb some of the blast, the Block 2 would have protection approaching that of an MRAP. New fuel tanks would be less prone to causing fires (using protection similar to that found in aircraft fuel tanks). There would be dozens of more minor improvements, based on user feedback. The Block 2 M2 would probably weigh about 35 tons, making it heavier than most World War II tanks (late model T-34s and M-4s).
The new version is not expected to show up for another 4-5 years. These upgrades represent a belief that the M-2 is an excellent, combat proven vehicle worth keeping around for a while. Over 4,000 M-2s were built, and about 2,300 similar M-3s (a recon version with more gear and fewer passengers). It's unclear how many would be upgraded.