Наряд is either a specific task or a group of people assigned to a specific task. It can also be a document stating that a specific task must be carried out. Note: this word is in no way reserved for military/police use only, although it is used most often there.

Наряд на получение груза - A document that states you're allowed to unload the goods or a group of people assigned to this task.
Закрыть наряд - to complete the task
Караульный наряд - those who are to perform a sentry job
Наряд полиции - those who are to actively carry out the police duties. People who patrol the streets, roads etc, as opposed to those with a desk job.