 There also was a production run in 1953-54, of 27,218 "militarized" H-500's, designated R-520/URR, ordered by the U.S. government for the Korean conflict.This set added a sixth tube, the 50A1, to eliminate power fluctuations.After 1953, there was competition to the Trans-Oceanic from both Hallicrafters, with their 'Trans-World' series sets, and RCA, with their 'Strato-World' models.