A mathematical model is presented for the retardation of the Werthamer functional for the Josephson tunneling junction to treat the current controlled case. Computational results concerning the current‐voltage characteristic make visible an enhanced hysteresis due to the nonlinear frequency response of the tunneling current. In addition, the irreversible flux transition in a SQUID is analyzed: the flux quantum transition time is found to be shorter than predicted by quasiadiabatic models.