: Casualty Rates by Branch- Armies are divided into "branches": infantry, armor, artillery and support. 

Infantry is the branch with the most casualties, usually 50-80 percent. Infantry divisions with no tanks and minimal artillery suffer the most infantry casualties. Industrialized nations provide even their infantry divisions with 100-200 tanks and over a hundred artillery pieces. Infantry includes reconnaissance troops. Contemporary divisions consist of less than 25-50 percent infantry, often closer to one third. As recently as World War II, infantry comprised nearly two thirds of personnel in most divisions. 

Armor is the branch with the most firepower per man. Armor combat strength declines rapidly because the heavy combat vehicles tend to break down easily. In combat divisions today, armor troops comprise 5-30 percent of manpower. Depending on the type of division, armor troops will suffer 10-30 percent of the casualties. 

Artillery is the combat branch that inflicts the most casualties and receives the least. As the armor and infantry waste away in combat, artillery becomes the principal provider of combat power. In combat divisions today, armor troops comprise 10-25 percent of manpower and suffer 5-10 percent of the casualties.

The remaining manpower includes the support troops that may come under fire but do not regularly confront the enemy in combat. These troops comprise 25-35 percent of division manpower and suffer 1-3 percent of the casualties.

For the most part, these soldiers are found in battalions composed exclusively of troops of that branch. In some armies, artillery is often assigned to infantry units. Most armies equip their infantry units with mortars. Mortars, because of their short range and limited ammunition supplies, are considered infantry weapons. 

If a division is reported to have taken ten percent casualties, you can safely assume that the infantry have lost 20-25 percent of their strength. Tank units will generally lose strength in proportion to divisional losses (if the division has ten percent casualties, so do the tank battalions.) One new element in modern combat divisions (especially American ones) is an aviation brigade, with about 80 helicopters. This puts about 200 crewmen at risk. The risk isn't as much as you might think. During the Vietnam war, American helicopters flew 36 million sorties between 1966-71. Helicopters could fly a dozen or more sorties a day. The most commonly used choppers were the UH-1 and AH-1 (just now being phased out of U.S. service, but still widely used around the world.) On average, every 100,000 sorties saw 13 helicopters crash. But 55 percent of these were not combat related. For every hundred helicopters lost in combat, 145 crew and passengers were killed. For every hundred choppers lost for non-combat reasons, 89 people died. Helicopter crashes were more likely to have survivors because the choppers were usually operating close to the ground and capable of slowing down it's impact even with the engine shut down ("auto-rotation" of the rotor). Helicopters (the UH-60 and AH-64) are more resistant to damage and crew injury than their Vietnam era counterparts.