This is pretty remarkable. Apparently the best way to filter the results of a radar, even in as late as 1955 was to actually build the display CRT so that it just cut off part of the rear signal and fit in more of the forward signal. As opposed to some sort of tunable electronics that would allow you to change the scale and proportion displayed. This seems sort of wasteful since they obviously have front and rear signals that go out to 50 miles but are perfectly happy throwing that data away…
Off-Center Radar Picture Tube Gives Added Forward Vision
Ships can “see” 50 miles ahead and 30 miles behind with a special radar cathode-ray tube. General Electric, which developed it, calls it the “far-sighted, nearsighted radar indicator tube.” Engineers built the first tube by taking a standard 17-inch TV picture tube and installing a different phosphor screen and electron gun. Then they bent the glass neck of the tube five degrees so that the electron gun would give an off-center indication on the screen. The tube, used on Navy cargo vessels, gives added forward vision without the addition of a larger tube and a more expensive radar set.