The M3 cavalry fighting vehicle was essentially a restowed M2 Bradley infantry fighting vehicle. The M3 was the cavalry scout version, and its passenger compartment was occupied by two observers and more ammunition and missiles. Since the M3 lacked an infantry squad, it carried no firing port weapons, and the firing ports themselves were covered. The M3 retained the three periscopes between the cargo hatch and entry ramp and the periscopes along the sides of the vehicle.
The M3A1 incorporated the same improvements as the M2A1 Bradley. The CFV differed from the IFV in having NBC masks connected to the central filter for all five crewmen, instead of just the driver, gunner, and vehicle commander. The three periscopes on the rear deck were omitted in the M3A1, and replaced by four periscopes in the cargo hatch itself. The two periscopes on the right side of the passenger compartment were also deleted. (courtesy of afvdb.50megs.com/usa/m3bradley.html)