Most of the Estonian Defence Forces surrendered according to the orders of the Estonian government, believing that resistance was useless and were disarmed by the Red Army. Only the Estonian Independent Signal Battalion showed resistance to Red Army and Communist militia "People's Self-Defence" units in front of the XXI Grammar School in Tallinn on 21 June. As the Red Army brought in additional reinforcements supported by six armoured fighting vehicles, the battle lasted several hours until sundown. Finally the military resistance was ended with negotiations and the Independent Signal Battalion surrendered and was disarmed. There were two dead Estonian servicemen, Aleksei Männikus and Johannes Mandre, and several wounded on the Estonian side and about ten killed and more wounded on the Soviet side.
What was the name of the single unit that didn't surrender?
the Estonian Independent Signal Battalion