The U.S. Navy is equipping 40 of its CH-53E transport helicopters with lightweight armor kits that will provide protection from bullets and shell fragments. The CSA (Critical Systems Armor) uses lightweight materials (usually composites) and only protects areas of the helicopter known to be critical. These modular vehicle/aircraft composite armor systems have become increasingly popular in the last decade for helicopters and low flying fixed wing aircraft (like American AC-130 gunships). Flying low, aircraft are vulnerable to damage from rifles and machine-guns (especially the larger 12.7mm and 14.5mm ones), especially if the bullet his one of the crew or a vital component. These protection systems depend on two techniques to give maximum protection with minimal weight.
The most critical technique is to use an old World War II solution for protecting bombers from the effects of anti-aircraft fire (mainly the shell fragments). The American and British researchers used the newly developed operations research techniques to come up with a practical solution. Aircraft that returned from these missions were examined and the location of all damage was noted. Then the locations were counted and a drawing of the bomber type made with the damage locations noted. The armor was placed in those locations where there was no damage, as that’s where shell fragments obviously hit in all the thousands of bombers that were shot down. So with less than a ton of armor per aircraft, losses were noticeably reduced. This technique has been used to design protection systems for helicopters and other aircraft. The armor panels are placed where they would do the most good. The second difference is that the modern armor is not metal (like the World War II stuff) but lighter (and more expensive) composites. This stuff provides the same protection at half the weight. Thus a square meter of composite armor weighs about 37 kg (81.4 pounds or 8 pounds per square foot).
These armor kits are designed to be quickly attached. More, or less, armor can be installed, depending on what type of threat is expected. In many combat zones the enemy has few, if any, heavy (12.7mm and 14.5mm) machine-guns. This means the aircraft can reduce the weight of armor to be carried and the time involved in installing and uninstalling it. The weight is important and it has an impact on how long the aircraft can stay in the air. This type of armor has already been used in helicopters and larger transports like the C-130, C-141, and C-17.
The CH-53E entered service in the early 1980s and is in the process of being replaced by the CH-53K. This version is 16 percent heavier (at 42.3 tons) than the CH-53E and able to carry nearly twice as much (13.5 tons). The CH-53K will be much easier to maintain and cost about half as much per flight hour to operate. The K version will probably also get protection kits when they enter service before the end of the decade.