Phase locking of a vircator array driven by a relativistic magnetron in a pure master–slave configuration has been achieved. A single high voltage pulse drives the relativistic magnetron and the vircator array in series. Phase locking occurs for ∼40 ns. The time required to lock is &bartil;10 ns. the peak array power is &bartil;1 GW. The injection ratio, &rgr;, and allowable frequency difference, &Dgr;f, relationship required for phase locking is examined. The results suggest that the Adler’s inequality, &rgr;≳(Q/&Dgr;f)f, is a necessary, but not sufficient condition to predict phase locking. A hybrid configuration in which the driven vircators are also mutually connected together has also been attempted. Phase locking is observed with better phase stability than in the pure master–slave configuration.