When the Warsaw Pact invaded Czechoslovakia on 20 August 1968, Hammer's studies at the Academy were cut short. Hammer recorded a jazz trio live album at "The Domicile" in Munich on 30 August 1968. This was released as Maliny Maliny by the German label MPS Records. Hammer decided to move to the United States and resolved to become a citizen after receiving a scholarship at Berklee School of Music in Boston.