IMHO Radar is only any good if its foggy. It means nothing can surprise you on the surface.
It may help you track down one or two lone merchants or intercept a convoy a little quicker if you pick it up on radar before you see it or hear it.
A hydrophone dive every 6 hours is far better than radar.
Early versions of radar cover +10 to -10 deg. These are almost totally useless. If you have one of these sets them turn your u-boat in a total circle every 6 hours before your hydrophone check.
Later versions cover 360 deg.
Active sonar is useful for getting accurate range measurements if you are using manual TDC and no map updates. It can give you away to the enemy so use with care.
With the radar detectors you must remember that if you are detecting enemy radar, they already know where you are.
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