  We systematically study $K^+$ observables in nucleus-nucleus collisions at
1-2 A GeV within the Boltzmann-Uehling-Uhlenbeck (BUU) transport model. We
compare our calculations with the KaoS data on the kaon multiplicities and
spectra. In addition, the kaon collective flow is computed and compared with
the FOPI and KaoS data. We show, that the elliptic kaon flow measured recently
by the KaoS Collaboration is best described by using the Brown-Rho
parametrization of the kaon potential ($U_K(\rho_0) \simeq 30$ MeV).
