Complex sentence: Falling into the defences of Tobruk was the Australian 9th Division, and portions of several other units that had failed to escape before the advance of the Afrika Korps withdrew into Tobruk's defences as well, bringing the total force to 25,000 men.
Split into simpler sentences: Falling into the defences of Tobruk was the Australian 9th Division. In addition portions of a number of other units that had failed to escape before the advance of the Afrika Korps withdrew into Tobruk's defences as well, bringing the total force to 25,000 men.