Ever wondered why you can see so well the machine gun fire in those action movies? That’s tracer ammunition in action for you, though this specialized projectile type has very specific uses outside of the movie industry as well…
Tracers are basically bullets or projectiles with a small built-in pyrotechnic charge, usually including phosphorus or magnesium. As this additional charge burns brightly mid air, it makes the projectile trajectory visible to the naked eye in daylight, and extremely bright at night time. The NATO and US standards burn typically red, while the Russian and Chinese tracers generate a green light. Tracer bullets are typically marked with a different colored projectile tip.
We can differentiate 3 main variants: bright-, subdued- and dim tracers. Bright is the standard version that – surprise! – burns brightly from start to finish. Tracer works both ways however and it can also easily give away the position of the soldier, thus other improved versions had to be developed. The subdued tracer is a great example for this, as it lights up only after about a 100 yards or so, protecting the gunners position. Dim tracers go even further than this, as they are mostly visible by night vision equipment only.
Their use is actually surprisingly varied, though the main goal is simple – to help the gunners correct their aim without having to look into their sights. For the longest time soldiers had to correct their aim by watching the impact location of their bullets, however this became more and more difficult as the guns effective range increased. In the early 1900’s ammunition designers worked on a few radical concepts to make the bullets more visible, ranging from so called „spotlight” bullets that created a flash or smoke puff upon impact, to bullets leaving a trail of smoke. None of them were successful however, until the United Kingdom developed the first tracers in 1915.
Since it’s development it was mostly used with machine guns that could benefit from it the most. Typically every fifth round in the machine gun belts is tracer ammunition, to support the aim of the gunners. This was used both with portable and fixed machine guns –airplanes thought to especially benefit from it, as in the air there was no impact location from missed bullets, that the gunners could have used to adjust their aim. It turned out to be a double edged sword however, as it has been discovered that an optical illusion often tricked the gunners believing that the tracers hit the enemy aircraft, while in reality they zoomed past behind it, eventually forcing them to rely on their sights once again. In the end tracer became obsolete with most fighter aircraft, as these days missiles are the preferred air to air weapon, and the gun sights are radar directed anyway.
Tracers can work as excellent target markers as well, platoon- and squad leaders can use it to great effect to direct their solders’ fire to right target. Due to their nature they can also come in handy in emergency signalling. And that’s still not all! They also have been loaded towards the end of the machine gun belts to warn the gunners that they are about to run out of ammunition. Again this had a different effect on the ground and in the air, and once again aviation got the shorter side of the straw… During the Second World War the Soviet Air Force used tracers in this role, however as soon as the enemy pilots picked up on the meaning of this, the Soviet pilots ended up in very difficult situations. There was no such problem on the ground however, machine gun operators got typically covering fire until the reload was complete anyway.
Last but not least, these bullets have a mild incendiary effect as well thanks to their pyrotechnical charges, that can ignite flammable substances on impact. This was used to great effect against German Zeppelins in World War One. This is also the reason why the use of tracer ammunition is very restricted in most countries. Infamously the 2009 massive fires around Marseilles (France) were caused by a French Foreign Legion exercise, when the tracers ignited the bone dry vegetation in the summer heat.
HE Shell Types – High Explosive Destruction