Hi. My husband is in the army, so I can answer questions. The army is the land-based military branch.
What does he do in the army? 
Well, he's in the army reserves, so only really works during war or natural disasters.
I didn't know the army reserves assisted during natural disasters!
Emergency management
Emergency management is the organization and management of the resources and responsibilities for dealing with all humanitarian aspects of emergencies (preparedness, response, mitigation, and recovery). The aim is to reduce the harmful effects of all hazards, including disasters.
The World Health Organization defines an emergency as the state in which normal procedures are interrupted, and immediate measures need to be taken to prevent that state turning into a disaster. Thus, emergency management is crucial to avoid the disruption transforming into a disaster, which is
Standing army
A standing army, unlike a reserve army, is a permanent, often professional, army. It is composed of full-time soldiers (who may be either career soldiers or conscripts) and is not disbanded during times of peace. It differs from army reserves, who are enrolled for the long term, but activated only during wars or natural disasters, and temporary armies, which are raised from the civilian population only during a war or threat of war and disbanded once the war or threat is over.