Key point: Counterinsurgency operations have put troops at risk in novel ways.
Designing an armored vehicle always involves a three way compromise called the Iron Triangle between protection, mobility and firepower. Infantry Fighting Vehicles (IFVs) have traditionally been focused on mobility and firepower, with less emphasis on protection. But recent trends in conflicts have started to change this, as IFVs are mounting bigger and bigger guns and packing on more and more armor. A new class of vehicle is emerging: the heavy IFV.
The first IFVs were significantly more mobile than most main battle tanks (MBTs) in their era. In contrast to the T-55 and T-62, the BMP-1 could float across rivers and move faster on and off road. But the designers didn’t neglect the “fighting” aspect either, as it was meant to be able to tackle most MBTs of the era in ambush with its Malyutka Anti-Tank Guided Missile (ATGM). The American M2 Bradley also was amphibious and could handle tanks with its TOW ATGM.
The big trade-off they made was that they were not well armored at all. Bullets from a .50 caliber machine gun could go through the side a BMP-1 like butter and while the front was more resistant, almost any tank gun would go through it.
As the primary task of these vehicles was to support the infantry, this level of armor was considered acceptable. The mobility and firepower of the vehicle was considered to be more important because these early IFVs were designed to fight in a mechanized Cold War battlefield.
The key roles of the IFV were to provide Nuclear, Biological, and Chemical protection to the troops, protect them from small arms and artillery and bring a larger punch to the battlefield than what the infantry themselves could carry.
Adding more armor wouldn’t make them that much more effective at their role, and it would compromise their tactical mobility by getting rid of their quick-fording and swimming aspects. Soviet doctrine emphasized this capability: when crossing a water obstacle the BMPs were meant to cross first and secure the opposite shore before the tanks would attempt to snorkel or be ferried over.