 In November 1936, he volunteered to join "Sonderstab W", named after its commander General Helmuth Wilberg, for deployment in the Spanish Civil War.Following his arrival in Spain in mid-October 1936, Balthasar served with "Kampfgruppe" K/88 and "Aufklärungsgruppe" A/88 flying bomber and reconnaissance missions in Junkers Ju 52 and Heinkel He 70.On 16 March, he made a forced landing at Almorox following combat damage sustained by his He 70.