A bigger gun for lighter armored vehicles?

Earlier this year, I was intrigued to learn that Russia has decided to standardize on a 57mm. cannon (derived from the early-Cold-War-era AZP S-60 anti-aircraft cannon) for its next generation of infantry fighting vehicles (IFV's) and armored personnel carriers (APC's).  This is a development with both up- and downsides, and I've been trying to figure out the reasons behind the decision.

NATO and other armored vehicles are also in the process of being "up-gunned" in various countries, although not (yet) to as large a caliber as 57mm.  The US Bradley's M242 Bushmaster 25mm. cannon (using shells about 1" in diameter) proved very effective in both Gulf Wars, capable of destroying even former Soviet Cold War-era main battle tanks when engaging them from the side or rear.  Recent developments have included:

• "Up-gunning" some APC's (for example, the so-called "Dragoon" variant of the US Stryker) to a 30mm. (about 1¼" diameter) Mk44 Bushmaster II cannon.  The 30mm. caliber is already common in European APC's and IFV's.
• Britain and France have already gone beyond that caliber, adopting the 40mm (about 1½") CT40 cannon (shown below) for their next-generation APC's and scout armored cars.  The CT40 is also being discussed as a possible main gun for future US Bradley or Stryker variants, and/or their replacements.
   
• A 50mm. (about 2") cannon is under longer-term consideration for the US Army's proposed Optionally Manned Fighting Vehicle.

A 57mm. shell is approximately 2¼" in diameter.  It's no longer a light cannon, and its ammunition is considerably larger and heavier than that of a smaller-caliber weapon.  Vehicles can carry many hundreds (in some cases, even thousands) of rounds of the latter, but perhaps no more than 100-150 rounds for the bigger weapon.  That may pose difficulties in an extended combat situation, where resupply is difficult or dangerous.  Of course, each larger round is considerably more effective than each smaller one;  but they have to hit their target in order to be effective.  With the larger cannon, one can't afford to miss very often, for fear of wasting ammunition.  To be sure, modern targeting systems make it easier to get a first- or second-round hit;  but if they're disabled, one goes back to "ye olde Mark 1 eyeball" to hit something, which isn't nearly as accurate.  In combat in Angola in the 1980's, we carried, and could afford to spray, hundreds of rounds from the Ratel IFV's 20mm. cannon (and our Angolan and Cuban opponents could do likewise with their very effective ZU-23-2 23mm. weapons), both sides knowing that at least some of them were likely to connect.  With a modern large-caliber cannon, such profligate expenditure of ammunition simply won't work.  One can't carry enough rounds to be able to afford to miss with them.

Effectively, the larger-caliber main gun of an IFV or APC will no longer be a primarily anti-personnel weapon.  It'll be there to take on enemy IFV's, APC's, and perhaps even main battle tanks, as well as gun emplacements, static defenses, and defensive missile teams.  The latter is a primary reason for the heavier caliber gun - its longer range.  When highly effective infantry-portable missiles such as the Javelin can reach out to 2½ miles (in its latest version), an armored vehicle simply daren't get within range of them.  It would be too easily neutralized.  It has to keep its distance and shoot at the missile teams, vehicles and emplacements until it's sure it can advance in relative safety.

That also means it has to rely on sophisticated optical, infra-red and laser sighting systems to detect the enemy, even when well camouflaged, and ensure its rounds will be on target.  Therein lies another vulnerability.  If an enemy can disable or destroy those sighting systems, the long range of the vehicle's gun simply won't matter - it won't be able to put its rounds where they need to go.  Even relatively unsophisticated weapons, such as machine-gun fire or anti-personnel "beehive" or canister rounds fired from a cannon or recoilless rifle, can accomplish this, even if they can't penetrate the vehicle itself.  I witnessed the effectiveness of such tactics and equipment during the 1980's.  Airburst artillery rounds can accomplish the same thing, even without scoring a direct hit.

Some might argue that such a vehicle, armed with such a weapon, can simply "stand off" from such dangers, and eliminate them before getting close enough for them to be effective.  That's all very well if the battlefield allows it, and if one's sighting systems allow such threats to be detected at stand-off ranges:  but if that's not the case, then the advantage of the heavier cannon is reduced or even eliminated.  In a bush warfare environment in Angola, where line-of-sight was frequently measured in tens of yards only, I saw UNITA guerrillas dig narrow foxholes, so deep that a fighter could stand upright in one with his head below the surface of the ground.  No thermal or other sight would detect them in such fighting positions, and they were almost invulnerable to air raids or artillery bombardment.  They could (and did) remain out of sight until enemy vehicles had passed overhead, then climb onto a box or other step in the bottom of the hole and send an RPG-7 grenade up the tailpipe of whatever had just passed - be it a tank, an APC or a truck.  The Cubans and Angolans lost more than a few vehicles that way (not to mention their crews).  In urban warfare, there are similarly short lines of sight.  An enemy can remain hidden in rubble or ruined buildings until a tank or APC is so close he can almost reach out and touch it, then use a weapon against it.  Even a primitive Molotov cocktail is likely to damage or destroy delicate sighting systems, rendering the vehicle's weapons combat-ineffective.

The traditional answer to such threats has been to have infantry advance with armored vehicles, each protecting the other.  However, a bigger, heavier cannon on the vehicle may make it dangerous for troops to be too close, due to increased blast, noise, and the larger visual signature (dust kicked up by firing, etc., making it easier for the enemy to direct counter-fire).  There's also the issue of active protective systems, such as the well-known Israeli Trophy (soon to enter service with the US Army).  These can effectively defend vehicles against incoming rockets and missiles;  but their explosion might also injure or kill infantry moving close to the vehicle.  See for yourself in the actual combat footage below.

There has so far been limited combat experience with infantry moving in close proximity to such systems.  I expect it to be problematic as more of them come online.  Infantry may be supposed to move alongside vehicles, but if that means they're more likely to be injured or killed by the vehicles' defensive systems, then no matter what their orders may be, they won't do so.  They're not stupid!

I suppose these larger cannon are trying to answer a question that hasn't yet been properly - or, at least, openly - discussed.  In future warfare, as far as front-line combat is concerned, does infantry still have a role on the battlefield?  Is combat going to develop into a slugging match between vehicles, and possibly between unmanned systems or artificial-intelligence autonomous weapons systems?  If so, the new, heavier cannon on IFV's and APC's make sense.  If not - if infantry still have their traditional role in battle - then I'm not so sure.  I think a lot of this will have to be worked out in actual combat, where people learn the hard way what works and what doesn't, and pay in blood and bone to find out.  Certainly, the US armed forces are having to rethink their equipment and training after almost two decades of fighting guerrilla-style opponents in Afghanistan and Iraq.  Conventional adversaries won't fight the same way, will be equipped with much heavier and more capable weapons, and will need different tactics and equipment to prevail against them.  Firepower alone won't do it.

It's an interesting conundrum.

Peter