Survival knives are intened for survival purposes when lost in a wilderness environment. Military units issue some type of survival knife to pilots in the event they may be shot down. Hunters, hikers, other outdoor sport enthusiasts, and adolescent boys also purchase and use great numbers of commercial survival knives. Some survival knives are heavy-bladed and thick; others are more lightweight or fold in order to save weight and bulk as part of a larger survival kit. Their functions often include serving as a hunting knife.