Flak jacket A flak jacket or flak vest is a form of body armor designed to provide protection from case fragments ( " frag " ) from high explosive weaponry , such as anti - aircraft artillery ( " flak " ) , grenades , some round shot used in shotguns and land mines and other lower - velocity projectile s . It is not designed to protect against bullets fired from small - arms such as rifles or handguns . However , certain flak jackets are able to sustain certain gunshots , dependent on the armor , the gun , and the distance that the bullet has travelled . The term " flak jacket " is often colloquially applied to newer body armor featuring protection against small arms projectiles , but the original usage predated the existence of functional bulletproof vests and the two are not interchangeable in performance . History . Anecdotes describing garments designed to protect the wearer from penetrating weapons can be found far back into recorded history . Two types of protective garment from the American Civil War in the 1860s had a basic design similar to the flak jacket or ballistic armor of modern times in that solid plates were used as the main ballistic protection . The " Soldiers ' Bullet Proof Vest " was manufactured by the G . & D . Cook & Company of New Haven , Connecticut . It consisted of two pieces of steel inserted into the pockets of a regular black military vest . Versions for infantry weighed 3 ½ pounds while a version for cavalry and artillery weighed 7 pounds . They sold for $ 5 – $ 7 . A more medieval - looking type of armor was made by the Atwater Armor Company , also of New Haven . It consisted of four large plates of steel held on the body by broad metal hooks over the shoulders and a belt around the waist . The Atwater vest was heavier than the Cook models and cost about twice as much . During World War I , a number of British and American officers recognized that many casualties could be avoided if effective armor were available . Isolated efforts at developing armor were made , and soldiers could make individual purchases or efforts , but there was no armor issued to the troops . As it is today , issues of weight , cost , availability of materials and / or environmental stability complicated the issue of developing armor that would also be effective . For example , soft armor made of silk was tried on a small scale based on Japanese designs , but this material did not last well under the harsh environmental conditions . The first usage of the term “ flak jacket ” refers to the armour originally developed by the Wilkinson Sword company during World War II to help protect Royal Air Force ( RAF ) aircrew from the flying debris and shrapnel thrown by German anti - aircraft gun s ' high - explosive shells ( flak itself is an abbreviation for the German word " Fliegerabwehrkanone " ( " anti - aircraft gun " ) ) . The idea for the flak jacket came from Col . Malcolm C . Grow , Surgeon of the US Eighth Air Force in Britain . He thought that many wounds he was treating could have been prevented by some kind of light armor . In 1943 he was awarded the Legion of Merit for developing the flak vest . Unfortunately , flak jackets proved to be too bulky for wear within the confines of the RAF ' s standard bomber aircraft , the Avro Lancaster . The Royal Air Force subsequently offered the jackets to the United States Army Air Forces , which adopted them as a Defense Standard . During World War II , flak jackets and steel helmets were worn by US Navy personnel on aircraft carriers during battle , since the ships and especially their flight decks offered little protection for their crew . The jackets were supposed to protect against shrapnel and heat . Ballistic protection . Col . Grow ’ s request to the Wilkinson Sword company was to develop a vest that could stop a . 45 caliber round fired at close range . Although flak jackets offered some basic protection against small caliber bullets and shell fragments ( which was obviously welcomed by their users ) , ultimately they proved to be less effective than hoped . Flak jackets are now generally considered to be inferior to body armor . It was claimed that the M - 1951 field jacket could stop a 90 grain 7 . 62×25mm Tokarev pistol round at the muzzle of the gun . However , even the Vietnam era revised flak jacket was not really designed to stop an AK - 47 round ( a 7 . 62×39mm ) fired at close range . Nevertheless , it did a good job of stopping shell blasts , rocket fragments , snake bites , fire ant bites , prickly thorn and slower bullets fired at a moderate range . It was not until 1970 that the U . S . National Institute of Justice , which now publishes test and performance standards for body armor , began a deliberate program to develop body armor for law enforcement personnel that would be effective against specific threats that were common causes of officer injury and death . At the time that included . 38 Special and . 22 long rifle bullets , in particular , and also bullets from 9 mm , . 45 , and . 32 caliber firearms . Materials . The flak jacket consisted of manganese steel plates sewn into a waistcoat made of ballistic nylon ( a material engineered by the DuPont company ) ; therefore , flak jackets functioned as an evolved form of plate armour or brigandine . The first flak jacket weighed 22 pounds . During the Korean and Vietnam wars , the flak jacket was changed and the manganese steel plates were replaced by other materials . The U . S . Army ' s vests ( Body Armor , Fragmentation Protective , Vest M69 ) weighed under eight pounds and were made of several layers of ballistic nylon . The vests used by the U . S . Marines ( Vest , Armored M - 1955 ) weighed more than ten pounds and were a combination of ballistic nylon layers and fiberglass plates known as Doron . Doron was made of the fiberglass fibers in an ethyl cellulose resin under high pressure . It was named after then Col . Georges F . Doriot , then director of the Military Planning Division , Office of the Quartermaster General . The generation of armor developed in the 1970s through the National Institute of Justice incorporated layers of soft armor in the form of DuPont ’ s Kevlar fabric , which has since become synonymous with ballistic protection and a general term used for several similar ( aramid - based ) materials .