Complex sentence: On 11 April, the two monitors were forced to withdraw from Dubovac towards Belgrade, during which they came under repeated attacks by Junkers Ju 87 "Stuka" dive bombers.
Split into simpler sentences: On 11 April, the two monitors were forced to withdraw from Dubovac towards Belgrade. During their withdrawal, they came under repeated attacks by Junkers Ju 87 "Stuka" dive bombers.