We will review the design of the dual‐mode X‐band rf system proposed for the Next Linear Collider (NLC). Recent experimental data are presented. The system is to produce 400 ns pulses with power levels up to 600 MW. A proof‐of‐principle experiment is being constructed at SLAC. Four 50 MW klystrons will power a fully dual‐moded resonance delay line pulse compression system. Both the transfer line and the delay lines are dual‐moded. The modes carried by the transfer line are controlled by the rf phases of the different klystrons. The modes in the delay lines are controlled by a set of mode converters at the input and the end of each delay line. By manipulating the modes in the transfer line, one can achieve either no pulse compression or a pulse compression ratio of 4. The total output power will be 200 MW for 1.6 microseconds or 600 MW for 400 nanoseconds. © 2003 American Institute of Physics