Hogan's Heroes had its best ratings during the first 1⁄3 of its run: A 24.9 rating during season 1 (when it ranked at 9th place), and a 21.8 rating during season 2 (when it ranked 17th). After that, the CBS comedy series already fell out of the Nielsen Top 30.
How was Hogan's Heroes able to keep going for another four seasons since then? One would assume that HH must have fallen to the bottom of the Nielsen charts by the time of its 1971 cancellation. Ratings info for non-Top-30 programs before the 1970s is scarce.
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"When the run of a network TV show has ended, some go out with a bang, some with a whimper, but all are...Future Endeavored."
Apparently it was shifted to Saturday night at 900 PM in its third season and lost a number of younger viewers; competing with movies on NBC . Especially those with big name stars. But it did respectable in its time slot. Howard Caine felt CBS really wanted to kill it win they scheduled it opposite Disney.