From early war bombing methods for Allied pilots:

Approaching a target wreathed in cloud, there were only two possibilities: to descend to recklessly low level to seek visual identification- which cost many crews their lives - or to bomb on ETA - estimated time of arrival over the target, judged from the last pinpoint, perhaps hundreds of miles back.

This was the commonest course among mediocre crews, who had their own saying: " He who bombs on ETA lives to fly another day."

From Bomber Command by Hastings

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