The Junkers JU-87 Stuka was the most famous of all planes used by the Germans as a sturzkamfflugzeug (divebomber). The Stuka was designed strictly as an army cooperation divebomber at the urging of General Ernst Udet. It is instantly recognisable with its inverted gull-wings, and fixed-undercarriage. The Ju 87 was ugly, sturdy, accurate, but very vulnerable to enemy fighters. The Germans learned in the Battle of Britain that its use demanded air superiority. It was too slow, unmanoeuverable and underarmed, but its effectiveness in destroying vehicles, fortifications or ships, or just scaring people, was undoubted. Its accuracy was high when in a full dive that was up to 80 degrees. Once the bomb was released it used an automatic pull-up system to ensure that the plane pulled out of the dive even if the pilot blacked out from the high g forces. The Germans fitted the wheel covers with sirens that were used once the planes went into a dive to shatter the morale of enemy troops and civilians. They also fitted whistles onto the fins of the bombs to ensure that the recipients knew just when the bombs were released and could track them on the way down. Over 5700 Stukas were built.