MICV-70
The program may have ended there, but in 1968 a task force under the command of Major General George Casey urged the Army to continue with the program as information about the BMP started to become available. The Army once again turned to FMC, asking the impossible; lower cost, better mobility, lighter weight and better armor.
FMC responded with an entirely new vehicle, the XM723, based on the machinery of the US Marine Corps LVT-7. It featured a new steel/aluminum laminate armor that protected it against small arms up to the Soviet post-war 14.5 mm KPV heavy machine gun, which equipped the BTR-60 and BTR-80. Like the earlier MICV vehicles, the XM723 carried nine infantry that were seated back-to-back with rifle ports and vision blocks. When the XM800 program was cancelled in 1975 the scout role was switched to the new vehicle as well.
Throughout the development the M139 had proven disappointing and development of a new 20 mm weapon, the VRFWS-S "Bushmaster", started in order to replace it. As the VRFWS-S was a risky proposition, development went ahead with the existing M139 in the meantime. At the same time, testing demonstrated that there was too little room in the cabin for the M16 rifle to be used through the firing ports. A new weapon, the M231 Firing Port Weapon, was eventually adapted for this role from a small number of potential solutions. The M231 is essentially the M16 carbine with the stock removed.
Meanwhile a new task force, under Brigadier General Larkin, studied various 3rd party IFVs, including the German Marder, French AMX-10, and even examples of the BMP captured from Syria. A second study looked at vehicles with tank-like protection known as the "Heavy Infantry Vehicle", but this line was rejected on cost grounds as well as the added logistical requirements for everything from additional fuel to requiring bridging as they were too heavy to be made amphibious. Larkin's study ended in 1976, adding a further requirement that whatever vehicle was selected it should be available in a version equipped with the TOW missile for the light cavalry role.
FMC's XM723 seemed adaptable to both roles, and was renamed XM2 for the Infantry Fighting Vehicle and XM3 for the Cavalry Fighting Vehicle. The difference was primarily in the turret, with the XM2 having a single-man turret with the VRFWS-S cannon, and the XM3 including a larger two-man turret with both the cannon and a twin-tube TOW launcher. The primary reason for the two-man turret in the scout role was to give the commander a better field of view, in keeping with its battlefield observation role. During development the VRFWS-S was upgraded to a more powerful 25 mm caliber, emerging as the M242 Bushmaster. These vehicles evolved into the Bradley Fighting Vehicle that serves to this day.
Read more about this topic: MICV-65