Complex sentence: The defence allowed Army Detachment "Narwa" to escape from Estonia as the III (Germanic) SS Panzer Corps and the 11th Infantry Division abandoned their positions, unbeknownst to the Soviet 8th Army.
Split into simpler sentences: The defence allowed Army Detachment "Narwa" to escape from Estonia. The III (Germanic) SS Panzer Corps and the 11th Infantry Division abandoned their positions, unbeknownst to the Soviet 8th Army.