MAJ Ehrhart's paper, "Taking Back the Last Half Kilometer", has been making the rounds these past few days. It is an interesting paper on the tactical and technical deficiencies of the American and allied infantry in Afghanistan, using a 5.56mm carbine against enemy mortar attacks up to 2km away.
However, this is not a new problem. Mountain warfare experiences from WW2 and Indo-Pakistan wars have shown the necessity to engage enemy infantry beyond 500m. Some writers had warned, for example, that the US Marines reinforcing the Scandinavian flank during a Soviet invasion should bring the 7.62mm M-14 rifles with them to handle the mountainous terrain of Norway. For infantry warfare, there are two extremes: the close range (within 100m) of most infantry combat, and the long range (500m-1000m) requirements of mountain warfare.
To meet this combat requirement, the 6.8mm booster club would like to push the 6.8mm intermediate-intermediate cartridge onto the military. [Intermediate-intermediate because 5.56mm was originally sold as the intermediate cartridge.] They've been looking to get rid of the 5.56mm since its inception, and this is about as good a chance as they're going to get. The 6.5mm club is getting some airtime, too, but they're really too small compared to the 6.8mm club. However, due to the Army's historical foot-dragging on topics like this, this is not likely to happen. [Iraq was too close-quartered for their arguments to be effective, whereas our long war in Afghanistan will bring them many more instances of 5.56mm ineffectivenss.]
On the other hand, there are a couple of fixes we can implement fairly quickly, to meet this combat requirement of engaging enemies 500m to 1000m, with infantry squad weapons. The answers are the 40mm grenade and, surprise, the 5.56mm M-4 carbine.
Currently the 40x46mm unguided, low velocity grenade has a maximum range of 400m with an elevated trajectory. By putting a pair of pop-out fins and a laser seeker on the grenade, we can easily double the range of the grenade out to 800m. It's good timing, too, because the US Army just transitioned from the sliding breech M203 launcher to the swiveling breech M320 launcher. The M320 launcher can accommodate the increased length of the guidance package. Due to the low muzzle velocity of the grenade (76m/s), which is well-below that of common missiles, guidance integration should not be an issue. This development effort would take some time, but will be relatively fast due to the low technical risks involved. A smart grenade would be a "leap-ahead" technology the brass will love, so there will be few bureaucratic obstacles to its adoption. Long-term this grenade is the ideal solution to the mortar ambush scenario. The area effect of the grenade will easily suppress the insurgent mortar crews.
While we are waiting on the smart grenade, the infantry in the field can use their 5.56mm M-4 carbine to suppress the far-away enemy. But wait, you say, isn't the whole problem we're facing that 5.56x45mm cannot reach beyond 500m? Actually, the 5.56mm can go all the way out to 2,000m. The only problem is that you cannot aim it accurately beyond 500m, because the bullet is too light and will drift off course. Back in World War I, the bolt-action rifles all had sights that ranged out to 1,000m, even though few people can aim that far without scopes. [Even today, AK-47 sights can adjust out to 1,000m.] Back then, infantry often had to provide its own fire support, sometimes without help from artillery. The whole regiment would line up, adjust the sights out to 1km, then fire at that target together. The massed rifle fire would blanket that far away target with a rain of lead bullets. The mass fire compensates for the inaccuracy of the individual rifle and man at that distance. Similarly, the machine guns of the era had long range sight markings for indirect-fire, area suppressions. Machine guns were organized in batteries then, and they would mass arcing fire on targets kilometers away.
We can do the same thing today. A squad or two can mass their fire against the suspected insurgent position. A squad of M-4s can generate the fire volume of a WW1 battalion by aiming together. With a bit of range experimentation, you can easily figure out how to shoot out to 1km. I did a bit of calculation and I found that you probably need to elevate your muzzle by 0.28 degrees to shoot 1km. According to online ballistic calculators, you will need about a 1 degree elevation. So work with that and try it out. A bit of Kentucky windage in the field will get you close enough to the target to suppress them. A rain of steel and lead will make the insurgents think twice of mortaring you.
Of course, you still need to close with and assault the enemy. A squad can suppress the position while other squads maneuver to close the distance. You will need at least a squad to generate the fire volume to suppress out to 1km.
Some people will say that the 5.56mm cartridge does not have enough energy to kill a man at 1km. However, try standing out there, without a helmet, while bullets rain down around you. The 5.56mm still has enough energy to lodge inside your braincase at that distance.
So, write your Congresscritters to start this smart grenade program. In the meantime, start experimenting with the sights of your M-4 carbine. Your squad can still suppress that insurgent mortar team, despite what your training told you.
ETA: links and paragraph breaks