In civilian usage, a casualty is a person who is killed, wounded or injured by some event, and is usually used to describe multiple deaths and injuries due to violent incidents or disasters. Casualties is sometimes misunderstood to mean fatalities, but non-fatal injuries are also casualties.
In military usage, a casualty is a person in service killed in action, killed by disease, disabled by injuries, disabled by psychological trauma, captured, deserted, or missing, but not someone who sustains injuries which do not prevent them from fighting. Any casualty is no longer available for the immediate battle or campaign, the major consideration in combat, and the reason for lumping together all these different cases. The word has been used in a military context since at least 1513.
The story is presented as a flashback of Max Eriksson, a Vietnam veteran. A platoon of American soldiers is on patrol when they are suddenly attacked by the Viet Cong. While on flank security, the ground cracks under Eriksson as he is above a Viet Cong tunnel. Sergeant Tony Meserve pulls Eriksson out of the hole and eventually, the Americans stave off the attack.
The platoon takes a break outside a river village in the Central Highlands. While relaxing and joking around, one of the platoon members, Specialist 4 "Brownie" Brown, is killed when the Viet Cong ambushes them. Shortly afterward, Private First Class Antonio Diaz arrives as Brownie's replacement.
Marines, also known as a marine corps and naval infantry, are an infantry force that specializes in the support of naval and army operations on land and at sea, as well as the execution of their own operations. In the majority of countries, the marine force is part of the navy, but it can also be under the army like the Troupes de marine (French Marines) and Givati Brigade (Israeli Marines), or form an independent armed service branch like the United States Marine Corps and Royal Marines.
Historically, tasks undertaken by marines have included providing protection from war while at sea, reflecting the pressed nature of the ships' company and the risk of mutiny. Other tasks would include boarding of vessels during combat or capture of prize ships and providing manpower for raiding ashore in support of the naval objectives.
With the industrialization of warfare in the 20th century the scale of landing operations increased; this brought with it an increased likelihood of opposition and a need for co-ordination of various military elements. Marine forces evolved to specialize in the skills and capabilities required for amphibious warfare.