Fortunately for both, neither the Soviet Army nor the U.S. Army had to test the infantry fighting vehicle concept on a nuclear battlefield. It’s a testament to the shifting challenges of warfare that a vehicle designed in Moscow in 1955 could indirectly affect a vehicle serving in Iraq in 2009. We don’t know what will replace the M2 Bradley, and we know even less about where such a replacement might be called upon to fight. One thing’s for sure: whatever it is, it can probably do without port-firing weapons.

In the 1960s, the Soviet Army made a fateful decision: it could live with tactical nuclear warfare. In the wake of the bombings of Hiroshima and Nagasaki, armies on both sides of the Iron Curtain came to believe that nukes had become the dominant weapon in warfare. Yet, as time wore on, they also came to believe that fast-moving armies protected against radiation could still prevail on the battlefield. The result was, in a roundabout way, America’s first infantry fighting vehicle: the M2 Bradley.

The Soviet Army of the 1950s had invested a great deal in massive, highly mechanized forces. Nuclear weapons, on the other hand, with their overwhelming firepower, threatened to negate large armies—and large navies and large air forces too for that matter. But as the dominant land power of the twentieth century, Moscow could not give up its numerically superior armies. The answer was to figure out a way to fight through a nuclear war.

Soviet tanks had natural protection against the heat and blast of a nuclear weapon, but Soviet infantry in their open-topped armored personnel carriers were vulnerable. The result was the boyevaya mashina pekhoty (BMP), or infantry fighting vehicle (IFV). The BMP could carry an entire infantry squad and was armed with a seventy-three-millimeter gun launcher and AT-3 Sagger antitank missile. Infantry traveling inside could even shoot their AK-47 rifles through portholes on the side—although they rarely if ever did. Rather than dismounting during attacks, the Red Army infantry would fight mounted, and thus advance across the battlefield quickly—too quickly to be bracketed by tactical nuclear weapons.

In the West, military analysts were belatedly coming around to the same conclusion. The Army was still operating M113 armored personnel carriers. Lightly armed and armored, the M113’s sole job was to transport infantry to edge of battle, whereupon they would dismount and attack on foot. As the Soviets pointed out, however, the slow pace of dismounted infantry attacks virtually invited tactical nuclear weapons.

The United States Army decided it needed an infantry fighting vehicle of its own. The first effort, Mechanized Infantry Combat Vehicle–1965 (MICV-65) was based on the M109 self-propelled howitzer chassis. Equipped with a turret and twenty-millimeter cannon, it was eventually discarded as too heavy for air transport, and too slow to keep up with the German-American MBT-70 main battle tank.

This was one of the first dilemmas behind the IFV. Infantry fighting vehicles had to be large to accommodate a full infantry squad, and they should be heavily armored—after all, up to twelve people would ride inside, three times as many as inside a tank. But the larger and better protected they got, the slower and less agile they became.

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At the same time, the U.S. Army staked out a requirement for a new Armed Reconnaissance Scout Vehicle to equip scout platoons and armored cavalry regiments. In a cost-saving move, the Army decided to merge the IFV and ARSV programs into a single vehicle with both infantry fighting vehicle and scout vehicle variants. Here was another dilemma: an IFV with a manned turret would stand tall—taller than a tank—and stand out on the battlefield. The ARSV, on the other hand would be better served by a low-profile vehicle: the better to observe the battlefield undetected if necessary.

The prototype vehicle, known as XM723, was unveiled in 1973. Designed by the FMC Corporation, it weighed twenty-one tons, had a crew of three and carried nine troops. Its armor could withstand hits from the Soviet 14.5-millimeter KPV heavy machine gun. Like the BMP it had a small, one-man turret equipped with a twenty-millimeter cannon. Soldiers riding in the back of the XM723 would, like their Red Army counterparts, still fire weapons but instead of using their own weapons would use a modified M16, the M231 port-firing weapon.

The dilemmas—and compromises—continued piling up. The gun was upgraded from twenty-millimeter to twenty-five-millimeter, the better for the scout vehicle to deal with light armored threats. Unlike the M113, the XM723 would be much more likely to see enemy tanks, and so a box launcher was added to a new, larger two-man turret that carried two TOW long-range antitank missiles in the ready position. This made more sense in the scout version than the infantry fighting vehicle, but the Army decreed both would use a common turret, forcing the TOW launchers on the infantry.

The larger turret and larger weapons made the vehicle larger and heavier. The M242 Bushmaster cannon and TOW missile launchers demanded room for the new ammunition. Three seats for infantrymen were deleted, replaced with 7.62- and twenty-five-millimeter ammunition, plus TOW missile rounds.

That was fine for the scout version, which only needed room for two dismounted scout soldiers and ammunition, but it reduced the number of infantry dismounts in the IFV version from nine to six. While this made the IFV better capable of destroying tanks, the loss of seating made it weaker in infantry dismounts—which were arguably the entire point of the vehicle. The port-firing weapons were never actually used.

Eventually the M723 was accepted for production and the resulting vehicle became known as the Bradley Fighting Vehicle, with two variants, the M2 Infantry Fighting Vehicle and the M3 Cavalry Fighting Vehicle. Although the M2 and M3 originated from different sets of requirements both vehicles appeared identical from the outside. While this has generally worked out—in the thirty-six years since production began, none of the forced design compromises on either vehicle has proven a show-stopper—one can’t help but wonder what would have happened had the Army designed two different vehicles.

Fortunately for both, neither the Soviet Army nor the U.S. Army had to test the infantry fighting vehicle concept on a nuclear battlefield. It’s a testament to the shifting challenges of warfare that a vehicle designed in Moscow in 1955 could indirectly affect a vehicle serving in Iraq in 2009. We don’t know what will replace the M2 Bradley, and we know even less about where such a replacement might be called upon to fight. One thing’s for sure: whatever it is, it can probably do without port-firing weapons.

Kyle Mizokami is a defense and national-security writer based in San Francisco who has appeared in the Diplomat, Foreign Policy, War is Boring and the Daily Beast. In 2009, he cofounded the defense and security blog Japan Security Watch. You can follow him on Twitter: @KyleMizokami.

Image: M2 Bradley Fighting Vehicle. Wikimedia Commons/U.S. Army