Probably the most iconic German aircraft during WWII, the Stuka dive bomber became the symbol of a string of successful campaigns in the early stages of the war. Hailed as the weapon of terror, it was the lightning that struck from the sky.

The German military doctrine, the Blitzkrieg – lightning war – swept across continental Europe. The Wehrmacht war machine indeed seemed unstoppable in 1939, when Stukas swarmed the sky above Poland.

Designated as the Junkers Ju 87 Sturzkampfflugzeug, the Stuka derived from a 1920s biplane, the American-produced Curtiss dive bomber that pioneered the dive-bombing technique.

The designer, Hermann Pohlmann, worked on a prototype throughout the first half of the 1930s. Test flights proved favorable in 1935, so Stukas were dispatched to Spain the following year, to take part in the battle. The Spanish Civil War was a training ground for German and Italian troops and equipment, as it served as an overture to WWII.

What specifically made these planes horrific were the two horns attached to the wings which produced a screeching sound once the aircraft was inbound for a strike. As the Stuka descended from the sky to drop its deadly load, the scream which accompanied it had a devastating effect on the morale of anyone who was on the ground.

It is unclear whether the idea originated from Adolf Hitler himself, or if the intimidation tactic was a brainchild of the notable flying ace and innovator, Ernst Udet, who was in charge of the Luftwaffe research and development office.

The two propeller-driven sirens with a diameter of 0.7 m (2.3 ft) were fitted on the B-1 model of the Ju 87, which was the first version of Stuka that went into mass production. They were either mounted on the wing’s leading edge, or on the front edge of the fixed main gear fairing.

The haunting horns were dubbed the “Jericho trumpets” by the Germans, who relied on the psychological effect of the noise to give them an edge against their opponents.

Like the Greeks and the Romans with their battle cries, or the Mongols, whose cavalry, heard from miles away, often chased enemies off the battlefield long before the fighting had begun, the German Stuka dive bombers were to some extent used similarly.

But the Jericho Trumpet had its downside too. It reduced the speed of the bomber by 15 miles-per-hour due to drag ― a flaw that proved deadly when facing AA guns and fighters. The lack of velocity, as well as the lack of proper defense against any potential threat apart from small arms, limited the use of Stukas to poorly defended ground convoys without air support.

The aircraft became outdated and vulnerable to Allied fighter planes. Apart from attacking military targets, it focused on raiding towns and villages, often deliberately causing civilian casualties.

After a while, the devastating effect of a screaming dive bomber was lost. Rather, it became a warning sign attached directly to the aircraft. Later versions were built without the Jericho Trumpets, and instead, aerial bombs were fitted with a whistling device for the same purpose.

Nevertheless, the sound was well remembered by the lucky ones who survived Stuka raids. It became so iconic that it was often mistakenly used in motion pictures to signify the sound of any WWII aircraft.

An imperfect aircraft, no doubt, but an effectively intimidating one ― the Stuka flew long after it was deemed outdated. Due to the lack of a proper replacement, the Ju 87 was constantly upgraded and refitted, but it never gained the edge over Allied and Soviet air superiority.

Its glory days were already over during the Battle of Britain, in 1940, when it exposed all its weaknesses when faced with a well-equipped and capable opponent.