The combat vest is based on the French armed forces "Cuirass de combat"' and consists of a sandwich of materials moulded to form a rigid shell. The outer layer of the sandwich is an ultra-light titanium alumide alloy to provide structural strength and ablative protection against lasers. Beneath this is a core, consisting of a layer of boron carbide resin bonded to a layer of graphite-composite carbon fibre. Boron carbide is an incredibly hard ceramic designed to shatter a bullet on impact while simultaneously forming a conoid base to absorb its energy. Beneath this, the carbon-fibre layer provides ballistic protection at the point of penetration by delaminating across a large area, so absorbing more energy. Finally, on the inside of the armour is woven liner made of 1,500 denier venlar fibres. This woven liner dissipates the remainder of the energy by deforming in the area of impact, and is also able to catch any spelling or fragmentation from the first three layers. Since any bullet fragment impact on the armour shell tends to compromise its integrity and ability to provide ballistic protection, it is standard practice to replace any affected section immediately.
In practice, the stopping power of armor is somewhat limited versus direct hits, particularly from high-velocity ball ammunition and HEAP small-arm rounds. However, it can be expected to stop low-powered ball ammunition and provide some protection against impact-fused explosive bullets and grenade or artillery fragments. Some stealth characteristics have also been included, such as curved and rounded surfaces to reduce radar signature, and infrared masking.
The armor comes issued in woodland camouflage but can be repainted to suit different terrain. The surname of the US Colonial Marine that the armor has been issued to is printed across the top portion of the front of the vest. Many Marines personalize their armor and this practice is mostly tolerated, unless the troops are in high profile positions. The armour has a PDT built into it with contact patches that monitor the Marines vital signs and are transmitted to the platoons Tactical Operations Centre.
The M3 armour comes in several components:
The main component is a rigid vest, which protects the thoractic-abdominal region, front and back, between the upper abdomen and lower neck. This comprises a two-piece clamshell secured by plastic clips. At the top of the clamshell, above each shoulder, is a rigid load-bearing arch from which hang the M3 Combat Webbing straps. These arches are padded beneath to protect the wearers shoulders when the armor is loaded with an IMP frame. Two segmented pieces attached by webbing straps protect the front and side of the shoulders. Inside the clamshell are remote biomonitors which measure the wearer's life signs, including heart-rate and breathing; an optic cable connects these to the PRC 489/4 transmitter in the M10 ballistic helmet.
Below the armored vest is a separate section which covers the front abdomen and groin. This is a flexible pad of rheological ballistic armor secured by a 'diaper' harness. A rigid armor plate is fixed to the lowest part of the pad to protect the genitals.
Leg armor consists of a pair of clamshell greaves which cover the whole of the lower leg from ankle to knee. The knee segments are articulated on webbing straps and tied around the leg above and at the back.
Velcro-lined heavy duty nylon webbing with side-release snap buckles. Comprises equipment belt with keepers, and suspender-style bandoleers that attach by snap straps to the load bearing shoulder pauldrons of the M3 Combat Armor's vest. Each bandoleer acts as grenade sling with four elastic loops for holding 30mm rifle grenades (18 total). A number of pouches can also be attached and these can be used for carrying items such as a bypass kit, personnel first aid kit, respirator, water hydration system or spare ammunition. A combat knife or pistol holster can also be attached to the webbing.