Two male patients asleep in hospital beds.
Two male patients asleep in hospital beds.

A military force requires people who are in excellent physical and mental condition. A soldier who is suffering from significant physical or mental disabilities is classified as undeployable and removed from active combat service. The reasons for removal from combat can range from something as obvious as a serious combat injury to invisible yet serious conditions such as post-traumatic stress disorder.

Injury

Serious physical injury, whether in the line of duty or as the result of unrelated activity, disqualifies a soldier from active duty. Shrapnel wounds, head injuries and loss of limbs all occur with distressing regularity in combat, and all remove the soldier from active combat, sometimes until they recover and sometimes permanently. Physical injury is frequently related to mental injury -- such as when a soldier develops anxiety or PTSD in response to the trauma of being wounded.

Mental Problems

Soldiers who have been in combat have a higher risk of mental instability. Conditions can include PTSD, depression and anxiety. Any of these conditions could disqualify a soldier from active duty because they would endanger both him and his fellow soldiers in combat. Many people who have latent mental instabilities are able to cope with them in a normal civilian environment but begin to have problems when subjected to the stress of combat. Combat situations can include unrelenting stress, fear, sleep deprivation and disorientation, all of which can contribute to the worsening of mental instabilities.

Drug Abuse

Drugs are a problem within the military just as they are in civilian life. In the military, drug problems range from pot smoking to prescription medication abuse. Substance abuse can also be related to other problems. For example, injured soldiers who receive painkillers to cope with their injuries sometimes become addicted to morphine, Demerol or Percoset. Soldiers who are identified as having drug problems are deemed non-deployable, although many soldiers on active duty continue to use drugs in unproductive ways.

Insubordination

The military relies on hierarchy and obedience. Soldiers who refuse to follow orders are quickly weeded out and deemed undeployable, and are usually subject to legal penalties as well. Insubordination can include refusing to follow orders, breaking rules or going AWOL. Some soldiers are disciplined within the military, while others who have committed serious crimes might be subject to legal trial as well. Incidents of insubordination tend to increase during prolonged and unpopular wars.