FYI: What's the difference between a flak jacket and a bulletproof vest?

Writing this from Afghanistan, FYI asked this question of a gang of burly South African mercenaries-cum-security guards propping up the bar at the Elbow Room, the capital Kabul's most happening nightspot. Before a bomb scare insisted we evacuate the place by the back door, they claimed the jacket and the vest to be one and the same. These days they're right, but that hasn't always been the case.

Flak jackets were first used by United States Army Air Corps gunners in Europe and Asia during the second world war. They were not bulletproof at all, but were provided to offer basic protection from airborne shrapnel (the word 'flak' is derived from the German Flugabwehrkanone, a type of anti-aircraft gun). The original garments were simple nylon vests with steel plates sewn into the lining.

Following the allied victory, the heavy and cumber-some jackets were redesigned for ground-combat use, and made their official debut during the 1950-53 Korean war. The new, lightweight jackets featured multiple layers of dense nylon instead of steel plates and weighed in at just 4kg. Following the conflict, a US Army report concluded the jackets had reduced the number of chest, back, and abdomen wounds that might have been inflicted on American troops by the North Koreans - and a large contingent of 'volunteer' Chinese sent into battle by Mao Zedong - by almost 70 per cent.

With the advent of the Vietnam war in the 60s, further modifications were made, but the jacket's raison d'etre remained the same: to shield the upper body from sharp metal fragments flying through the air. The idea of a jacket being bulletproof, especially with regard to fire from high-powered rifles, was considered far-fetched even as late as the early 70s, though the scientific solution had already been found.

In 1965, DuPont chemist Stephanie Kwolek - who was searching for a way to make radial car tyres lighter - had invented Kevlar. Only later did tests demonstrate the hi-tech material to be significantly more effective than nylon in dissipating the energy of bullets, and flak jackets began to be constructed from the super-tough, ultra-light fibre in 1975. Effectively, the flak jacket had evolved over time into what we now call the bulletproof vest. The modern, state-of-the-art flak jacket doesn't rely just on Kevlar (or rival fibres like Honeywell's Spectra). Inspired by the second world war garments, today's versions incorporate pouches for the armoured inserts, which are now made from aluminium-oxide ceramics.

The de rigueur jacket for the well-dressed, modern-day warrior about town is the Interceptor Multi-threat Body Armour System, manufactured by Point Blank Body Armor of Oakland Park, Florida. Even without the plates, this 4.5kg jacket is strong enough to stop a 9mm bullet at close range.