Modified magnetically insulated transmission line (MITL) has a dielectric filled break in the cathode part. Propagation of electromagnetic energy along this line is defined by the dielectric flashover and is inherently shock electromagnetic wave--the TEM--wave with a transverse current leakage. As a result of the evolution of this intricate process, high- power (1 - 104 GW) electron beam/electric pulse may be generated in the time range of 0.1 - 1 nsec. The purpose of this presentation is to show new experimental results gained from continuing study at the ZET accelerator in MRTI and at essentially different accelerator facility--the linear induction accelerator I-3000 (3-MeV, 20-kA, 20-ns) in ARRIEP. Newly, in both cases, REB's front shortening from 10 - 15 ns up to a value less than 1 ns has obtained. Besides experimental investigation, also theoretical studying of the process has been under way, for beginning, in the framework of the `telegraph equations'.