The dislocation dynamics of Gilman and Johnston are applied to the problem of elastic—plastic flow in Armco iron at very high strain rates. The dislocation velocity is assumed to follow the law v=v∞ exp(−τ0/τ); experimental data support this form of dependence and are used to determine the value of τ0. This value is in reasonable agreement with other measurements taken from Lüders band front velocities. A second quantity which can be evaluated is the initial density of dislocation lines, N0, which is found to be 2.0×108 cm−2.