Staff Writer (Updated: 7/18/2016):
The BMP-1 was primarily developed to replace the limited BTR-50 series vehicles (in particular the BTR-50P model) to which the much improved 8x8 wheeled BTR-60 Armored Personnel Carrier (APC) was also developed in conjunction and produced on an equally large scale alongside the more technologically-laden BMP-1 family. Both vehicles went on to see considerable usage overseas and across countless conflicts dotting the Cold War decades. Despite having entered Soviet Army service in 1966, the BMP-1 was first identified by the West in November of 1967 and is now generally recognized as the first "true" Infantry Fighting Vehicle (IFV), classified as such due to its ability to transport troops, disembarking them and then being able to operate as a stand-alone armored fighting vehicle (AFV). Thusly the BMP-1 was something of a revolutionary hybrid design incorporating the best assets of a light-class tank with the benefits of an armored personnel carrier - essentially creating a new sub-class of armored vehicle. Contemporary Western counterparts have since gone on to include the American Bradley, British Warrior and German Marder.
The BMP-1 designation is born of the words "Boyevaya Mashina Pekhoty 1" which translates to "Infantry Fighting Vehicle 1". Due to the limited nature of intelligence fielded by the West during the Cold War, the BMP-1 was initially recognized as the "M1967"before evolving into the "BMP-1" designation.
Design work on the BMP-1 series began in 1959-1960 through competition involving various concerns. The resulting winner became the "Obyekt 764" prototype which seemingly incorporated all of the design features sought by the Soviet Army (firepower, performance and protection). The first pilot vehicle was completed in 1964 and testing of more evolved models occurred into 1965 before the type was adopted in 1966 after having passed the requisite state trials.
The BMP-1 proved a departure from previous armored infantry carriers in that most early versions of such vehicle featured an open-air passenger cabin which exposed its infantry to all manner of battlefield dangers and environmental effects and hazards (namely the threat of nuclear war realistically persistent throughout the 1950s). The Soviet design incorporated a low-profile hull with extremely sloped glacis plate and basic operating crew of three (driver, gunner and commander). The engine was fitted to a front-right compartment to open the rear of the design for the passenger compartment and entry/exit through the unobstructed rear. The turret was set at center with unfettered views around the hull. The rear of the hull serviced eight infantry seated across two benches (four infantry per bench) facing outwards (fuel was stored between the two seat rows). The hull sides were given protected firing ports (four to a side) which allowed passengers the ability to help defend the vehicle through small arms fire from their own personal weapons (periscopes allowed for direct aiming though the ports themselves were not stabilized). Entry/access for the troops was through a pair of outward-opening hinged doors found at the rear face of the hull, each also sporting their own firing ports and aiming periscopes. The driver sat at the front-left in the hull with a personal hatch over his position and vision blocks for when the vehicle was "buttoned down". The turret maintained a hatch for the gunner while the commander resided in a special position just aft of the driver in the hull. As designed, and in keeping with common Soviet armored doctrine of the time, the BMP-1 was fully-amphibious and able to traverse open bodies of water with relative ease while being propelled about by the motion of its own tracks. Preparation consisted of raising a front-mounted trim vane and bilge pumps were turned on prior to any deep water entry. Water speeds totaled just 4.3 mph.