In the video, members of the Syrian rebel group Islamic Front are seen loading and firing the old artillery gun as part of an attack on the northern city of Ariha, the last important city in the Idlib region held by President Assad's forces.
Bild reports that this particular type of howitzer, the 10.5cm leFH18 (light field howitzer), was one of the most common artillery guns used by the German army (Wehrmacht) during the war.
It was designed by Rheinmetall at the end of the 1920s, and entered service with the Wehrmacht in 1935. From 1935-45 over 10,000 were produced.
They can fire 14kg artillery shells a distance of ten kilometers.
The howitzer was used all over Europe during the war, but it remains a mystery how the rebels got their hands on one in Syria.
“The Syrian army had a few in service. The rebels probably stole it from the army or maybe a museum,” expert Nic R. Jensen Jones told Bild.
“When fighters only have limited access to modern weapons, it's quite common that they resort to using older models,” he continued.
The civil war in Syria has been raging since the original unrest as part of the Arab Spring in 2011, and a wide variety of weaponry has been used.
Examples include the Karabiner 98k, the standard service rifle of the Wehrmacht, as well as others from Britain, the USA, France and Russia.
Syrian rebels sparked particular interest three years ago when they revealed they had 5,000 StG 44s, another German weapon from the Second World War, which is considered to be the first modern assault rifle.
“Either they were stolen by victorious Soviet troops and then given or sold to Syria, or delivered to Syria from the GDR, who used the StG 44 up until the early 1980s,” Jenzen-Jones suggested.
The estimated death toll of the civil war as of March is 220,000. Almost 4 million people have fled Syria since the beginning of the conflict, and a further 7.6 million have been displaced within the country.
The UN estimates that 12.2 million people are in need of humanitarian assistance in Syria.