# The Neural Net Tank Legend — Gwern Branwen

Source: https://gwern.net/tank . Cached excerpt for the ML-debugging skill (verbatim abstract passages).

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> A cautionary tale in artificial intelligence tells about researchers training an neural network (NN) to detect tanks in photographs, succeeding, only to realize the photographs had been collected under specific conditions for tanks/non-tanks and the NN had learned something useless like time of day. This story is often told to warn about the limits of algorithms and importance of data collection to avoid "dataset bias"/"data leakage" where the collected data can be solved using algorithms that do not generalize to the true data distribution, but the tank story is usually never sourced.

> I collate many extent versions dating back a quarter of a century to 1992 along with two NN-related anecdotes from the 1960s; their contradictions & details indicate a classic "urban legend", with a probable origin in a speculative question in the 1960s by Edward Fredkin at an AI conference about some early NN research, which was then classified & never followed up on.
