'Illusion' was the German occupation of Rab island in the northern part of the Adriatic Sea off the Croat coast of German-occupied Yugoslavia (19/23 March 1944).

At this time Generaloberst Dr Lothar Rendulic’s 2^nd Panzerarmee had decided to include Pag and Rab islands in its coastal defence system. Elements of Generalleutnant Johann Mickl’s 392^nd Division (kroatische) together with the 9^th Ustase Battalion secured Pag. On 20 March the 2^nd Kompanie of the 847^th Grenadierregiment was to land on Rab island from Senj from landing craft of the 771^st Pionierlandungsbataillon escorted by two torpedo boats and one corvette after the completion of their part in 'Biber'. These ex-Italian ships were to patrol between Cape Kalifront on Rab and Cape Lun on Pag to prevent any partisans from escaping in direction of Dugi island.

German intelligence lacked information that most units of partisans' 2^nd Coastal Naval Sector and the Jews who had remained on the island after their liberation from the Italian concentration camp at Kampor had left Rab on 3 March. Then the loss of TA 36 in 'Biber' prevented prevented the establishment of the planned naval blockade, compelling the Germans to rely on aircraft operating from the airfield at Zadar.

Between 19 and 23 March German aircraft made many attacks on partisan vessels in the Kornati archipelago and the coves of Dugi, sinking three motor sailing boats, two armed ships and one patrol boat.

On 21 March the Germans took control of Rab and started to fortify the island, which remained in Germans hands until April 1945.