Why would a rooster stop crowing?
Roosters crow due to a biological signal which sends signals to the brain. It is the same type of signal that helps a human body return to a normal temperature 1 hour before waking up or water lillies to close their leaves before the sun rises. The problem you are experiencing with your rooster may be a result of this signal no longer firing. It could be an age thing, sickness or disorientation. Also, if a rooster is not sleeping well throughout the day, exhaustion could be a factor. Lastly, scientists believe that crowing is a way roosters mark territory (like dogs urinating on everything). If there is no perceived competition to protect its hens, coop or territory - it may neglect to crow at all. Sorry I couldn't be more specific, but your question didn't have any supporting context or facts.
When there is no rooster among the hens one hen will usually try to take over the job of a rooster in so much as being a guardian. She will watch for danger and call to the hens to alert them. Sometimes even when there is a rooster, the dominant hen will mimic the crowing (or at least attempt to crow). She may even joust with the rooster, facing off with him and mock fighting.
It means that the sound of the crowing of the rooster (cockerel) in the mornings woke the soldiers up. The rooster acted like an alarm clock. 'Alarm clock' is therefore a metaphor for 'rooster'. Had the sentence read 'The far-off rooster was like an alarm clock for the sleeping soldiers' it would have been a simile.