MLRS is nicknamed "The grid-square destroyer" because an MLRS strike can roughly cover an entire 1km x 1km map quare with DPICM bomblets. If zombies were massed at a density of only one zombie per square meter, there would be 1,000,000 zombies in that area. There is no deficiency in the capacity of modern militaries to destroy large numbers quickly. Real wars are harder because the enemy is hard to find and/or shooting back. An unarmed "human wave" can be disposed of easily by any number of means. After reading the synopsis of the book on Wikipedia I must conclude that the author has completely no idea about military capability.

 

Even low tech -- hopelessly primitive 3rd world low tech -- militaries could achieve significant effects with options such as trenches filled with burning fuel, flamethrowers, IEDs, etc. More advanced 3rd world militaries with actual artillery would be even more effective even with conventional high explosive rounds - it just takes more of them and longer to do the same damage that ICM does. Note that artillery does not simply make a big boom, but physically sheds unprotected flesh with thousands of tiny splinters. Since the zombie hoard is presumably not taking cover to minimize the effects of such splinters, even ground bursts would be fairly effective. Airbursts would be even more so but require a fair degree of proficiency. Since the zombies are not shooting back it is not necessary to use indirect fire which requires a high degree of skill to be effective -- direct fire is fine. If the zombie hoard closes with the artillery unit, an option is HE rounds with time fuses dialed down to the minimum time, basically turning the howitzers into 155mm shotguns. There is a minimum range which if the hoard was able to reach would require the artillery be either moved or abandoned, but the numbers destroyed up to that point would be huge Also, though a theoretical zombie hoard would be able to overcome conventional countermobility measures such as concertina wire or barbed wire entanglements by simply climbing over the zombies entangled in the obstacle, arranging such defenses in depth would deplete the horde as more and more of the zombies became part of the landscape. Once immobilized the zombies could be wiped out at leisure. Even if these techniques didn't completely wipe out a zombie hoade, either because not every single one was killed by DPICM or cluster bomb bomlets or artillery, or because a flaming trench was eventually overwhelmed by bodies or whatever, it should at least thin their numbers enough that simple marksmanship would be sufficient to finish the rest off.

 

The following is a side trip from this discussions' main topic of military intervention in a zombie plague, but I feel compelled to point out that the author's lack of epedemiological understanding is mind boggling. Compared to a disease such as pandemic flu, a zombie virus would be easily and quickly contained. Simple biological spread from one person to another that requires such direct and obvious contact with the infected individual as a physical attack that wounds the victim has a number of consequences for a disease. It means that the number of people who are infected before the onset of the disease becomes obvous is negligible, unlike HIV. Also, the victim's behavior will cause people to avoid the person and report them to the authorities. It actually makes the disease easier to contain than conventional diseases because the victim does not require treatment by the medical personnel or family members which exposes additional people to conventional diseases. Since the victims are physically marked by the attack they can be readily identified and either quarantined or premptively killed.