A flack jacket is a form of protective clothing in the design of a vest. It is used to provide protection from shrapnel and other indirect low velocity projectiles. The flack jacket was originally developed by the Wilkinson Sword company during World War II to help protect the Royal Air Force air personnel from flying debris and shrapnel. The jacket consisted of manganese plates sewn into a waistcoat made of ballistic nylon- a material engineered by the DuPont Company. The flak jackets ended up being too bulky for wear within the confines of the RAFs standard bomber aircraft. The RAF subsequently offered the jackets to the United State Army Air Forces, who adopted them as a Defense Standard.

Every frontline soldier in Vietnam was issued a flak jacket as part of his combat kit. The flack jacket is worn over the upper body, and was designed to give protection against small arms fire, shrapnel, and flying debris.

The Marines usually wore the Vest, Armored, M-1955. It weighed just over 10 pounds and was made form a mixture of nylon and a special protective material know as Doron. Doron was first manufactured in 1943 by the DowChemical Company, and was created by bonding together glass filaments under high pressure, using a resin called methacrylate. This produced a hard but light weight material which could withstand ballistic impact at very short range. The vest was fitted with twenty three separate Doron plates, with layers of nylon to cushion the impact of a direct hit.

The Army's flak jacket was slightly different. It was called Body Armor, Fragmentation Protective, Vest M69. It reflected the Armys preference for nylon-aluminum rather than Doron. Protection was built up by means of layers of ballistic nylon filler, sealed in a waterproof vinyl plastic casing. The vest weighed under 8 pounds and was more comfortable than the M-1955, especially in the heat and humidity of Vietnam, although in both cases the habit of wearing the flak jacket unzipped to keep cool, undermined its value.

Unfortunately neither vest was really designed to stop an AK-47 round fired point blank, but they did a pretty good job of stopping shell blasts, rocket fragments, snake bites, fire ant bites, prickly thorn and the odd bullet that had just about run out of gas.

Now days the flak jackets have been replaced by Kevlar Body Armor and come in six different types that offer protecting all the way from a .22 caliber long range rifle up to an armor piercing rifle.