Activate or DeActivate requirement status of field based on another field
What you could do is make the military field not required. Then add your own validate function to the form with:

$form['#validate'][] = 'my_function_name';


Then in your function you can do a check e.g. 

function my_function_name*$form, &amp;$form_state){
  if($form_state['values']['my_gender_field'] == 'male' &amp;&amp; empty($form_state['values']['my_military_field'])){
     form_set_error('my_military_field', 'Military field is required');
  }
}


Or you could try using #states from the form API which has a 'required' option:
https://api.drupal.org/api/drupal/developer!topics!forms_api_reference.html/7.x#states