"Militaries came to destroy the infected, but what they found was unexpected"-Unknown victim of the virus, found in the Kin city hospital.
Much of the army (assumed to be the U.S.'s) was tasked with eliminating the infected and protecting civilians to ensure mankind's continued survival. When they failed, they applied martial law, and acted without orders to continue to save as many civilians as possible.
The military eventually lost too many personnel to the outbreak and ran out of supplies. After disbanding, most units became infected. Few have retained their gear [Helmets which provide damage reduction from small caliber weapons, such as pistols and low-powered rifles], but most only retained their clothes and possibly a spare magazine, which they have a chance to drop when killed. Military Zombies are more sensitive to sound, they run faster, and the ones with helmets can take more damage. This is probably due to the fact that before they were infected, they were trained for the military, thus making them more physically and mentally fit.