A flak jacket--also known as a “flak vest”--is a type of security vest designed to protect the wearer from projectiles penetrating the body. The term “flak” comes from the (thankfully) abbreviated German term for aircraft-defense gun “Fliegerabwehrkanone.”

Specifically, it was created to absorb or deflect case fragments from highly explosive rounds such as bombs, IEDs, anti-aircraft artillery, grenades, etc.

What A Flak Jacket Is (& Is Not)

Many will use the term “flak jacket” interchangeably with “bulletproof vest,” but this is technically a misstatement. The original flak jacket was, in fact, not designed to protect against small firearms (such as rifles and handguns).

Some flak vests were incidentally able to sustain gunshots depending on the angle, speed, and distance of the shot. Nevertheless, the materials technology of the time was not quite advanced enough to produce a consistent bullet-stopping vest. The construct of the flak jacket did, however, eventually inspire and give rise to modern-day bulletproof vests.

Interestingly, other than shape and metallurgy, the basic concept of the flak vest changed surprisingly little for most of history.

History of Body Armor

Various forms of body armor have served as a primitive version of the flak vest throughout history. These ancient flak armor designs usually fell into three categories:

(1) armour made of leather, fabric, or mixed layers of both (2) (chain)mail, made of interwoven rings of iron or steel (3) rigid armour made of metal, horn, wood, plastic, or some other similar tough and resistant material

The oldest known western armor is identified as a set of bronze-plated armour discovered in the Dendra village of Greece dated from around 1400 BC. Records indicate that body armor in the first category predates this find, but non-metallic armor materials likely did not survive the passage of time.

Ancient Chinese versions of the flak jacket were made out of 5-7 layers of rhino skin. Then the Celts designed mail--or “chainmail”--in 500 BC. This first-century version of a flak vest made of interlocking rings became a military staple for centuries.

The next advance in body armor came in the form of returning to metal-plated suits. Through the 13th-15th centuries, these were largely made of iron. By the 15th century, plate armor had become cheaper to produce. This was because chainmail was a trade specialty, and population changes due to the Black Death made labor more expensive.

How Gunpowder Changed the Armor Game

Besides upgrading to steel, body armor advances remained essentially the same throughout the Medieval and Renaissance periods in Europe. Ongoing improvements to early 15th century gunpowder weaponry meant the constant need to increase the thickness--and therefore weight--of body armor.

This continued until heavy-plated armor was abandoned in favor of mobility. Military leaders realized it was cheaper and more effective to have groups of unarmored men with early guns rather than outfitting knights with expensive armor.

Some Civil War soldiers purchased vests with metal plates sown in from individual makers, but these had varied effectiveness. No form of a flak jacket ever became standard-issue for these battles.

Additionally, most servicemen abandoned the vests due to their heavy weight over long marches and the stigma of being considered cowards by fellow troops.

Development of the M-1951 Flak Jacket

The flak jacket as it’s known today, came about as the brainchild of a surgeon in the Air Force during WWII. Col. Malcom C. Grow tallied the wounds received by his units, and determined that 70 percent were caused by low-velocity flak.

Seeing these as very preventable casualties, Grow, in partnership with Wilkinson Sword Company, consulted the New York’s Metropolitan Museum of Art to develop a security vest. “The design of Armor Vest M6, which is the latest standardized flyer’s armor, is based on one of the Museum’s brigandines dating from about 1400.”

His first recipients were to be Royal Air Force (RAF) servicemen who needed protection from debris and shell fragments by anti-aircraft guns. Unfortunately, these early models of the flak vest, however, proved too bulky for the RAF to wear. The first generation model had manganese steel plates sewn into a ballistic nylon waistcoat and weighed 22lbs.

The British offered 9,600 of some later-model flak jackets to the US military. These the U.S. issued to Navy personnel for the remainder of WWII to protect the very exposed flight deck crew.

The M1951 flak jacket model used during the Korean and Vietnam wars began the transition from steel to impact-resistant polymers. Metal was replaced with nylon padding around the upper body and plates of a fiberglass-based laminate called Doron that covered the lower chest, back, and abdomen.

From Flak Vest to Bulletproof Body Armor

Du Pont’s debut of Kevlar, the nylon-like polymer first produced in 1971, changed the game for personal protection. The final aspect of Colonel Grow’s original dream for the flak jacket could finally be realized: a security vest that could protect against close-range handheld firearm shots.

Kevlar became the foundational structure for the 1908’s Personnel Armor System for Ground Troops (PASGT). This was later replaced with the Interceptor Body Armor (IBA) system. IBA consists of both Kevlar and ceramic inserts for reinforced protection.

Altogether, this modern cousin to the original flak vest weighs in at about 16 pounds. While still hefty, the modern bulletproof vest provides protection against 7.62-mm full-metal-jacket rifle bullets—a level of protection that earlier security vest models could not match.