An S-band high power traveling-wave tube using a loop-coupled structure has been designed and tested. This structure, called the "\´centipede," was first suggested by Chodorow and Craig. The coupling between adjacent cavities is provided by means of several loops in each section. The tube characteristics are similar to the well-known "cloverleaf" with respect to high voltage and high peak power operation. The tube will be described and the test results presented. The first model of the centipede has the following characteristics: a saturated half-power bandwidth of approximately 500 Mc centered at 2900 Mc (or about 18 percent); a peak output power of 3 megawatts; a peak efficiency of 30 percent; and a saturated gain of approximately 26 db. The operating voltages ranged from 100 to

kv with a beam perveance of

. Design changes and test results of later models of the tube will also be presented.