12th century manuscript about Greek Fire in the Codex Skylitzes Matritensis, Bibliteca Nacional de Madrid
In the year 672 (loosely, we really don’t know when) the Byzantine empire stumbled upon one of their most valued inventions. A mixture of tars and minerals, the resulting liquid was both flammable and difficult to put out. It would ignite on water, it couldn’t be put out by water and it spread further as water was added to it, making it the Atomic Bomb of 7th century naval warfare. We assume now that it was a combination of crude oil and pine tars that the Byzantine empire had access to (Oil in the Black Sea and tars in Northern Anatolia) but the secret to Greek fire was lost with the empire.
The liquid was created just as Arabic armies began to attack the city of Constantinople, and it was largely responsible for the Roman victories in two of the sieges of Constantinople. The creation was timely enough that in his De Administrando Imperio, Emperor Constantine Porphyrogennetos (a later emperor in the 940s) told his son to never release the secret of the creation. That it must never be used on Christians, that it may only be made in Constantinople and that it was a gift to their empire from an angel of God, giving them a means of defeating the Muslim aggressors. He added that a chemist once tried to sell their secret to their enemies and was struck down by a pillar of flame when he next entered a Church. He and his son, along with nearly all others involved in the process kept the recipe tightly guarded, with only a handful of partial recipes and guesses existing now.
What made Greek Fire so effective was more than just the terrible nature of napalm while on a ship; it was the fact that they borrowed Greek technology to form a siphon and blast it. A long tube that would spray the fire made it the first real flamethrower in an era of bows and spears. There are accounts of soldiers even having handheld versions of the flamethrower, something akin to a large syringe with a burning tip that they could squirt the liquid fire from. Byzantines began to adapt the flamethrower into the very designs of their ships, with stories popping up about boats having metal lions and monsters at their prow. Inside these metal sculptures were tubing that allowed them to spray Greek Fire. Accounts of fully armored soldiers on ships leaping over the side of ships became more common, because they would prefer drowning over burning.
The creation made enough of an impact on the world that Western scholars called any weapon that used fire “Greek Fire”, regardless of their connection to Greece (Chinese and Arabic chemists were also using incendiaries around this time, Arabs were known to use grenades with a flamable liquid inside them, but it was never the same as Byzantine Greek Fire). By the 7th Crusade, there are accounts of Saracen troops using a device that shot a “spear of flame” at enemy troops and in the 1800s, an Armenian chemist was said to have approached the Ottoman government with a creation that appeared to be Greek Fire. When he refused to tell how it was made and demanded to be the one in charge of its deployment, things went sour and he was poisoned by Imperial officials without ever revealing his creation.
http://channel.nationalgeographic.com/channel/the-link/videos/greek-fire/ (this one is quite interesting)