British planners knew the nets extended to about thirty feet and chose a torpedo running depth of thirty-three feet. How they obtained that precise information remains unresolved in the research described here: the source had not been found in Andrew Boyd's study of British naval intelligence. Ordinary aerial photographs would not readily establish the submerged depth. One suggestion is that an officer or chief petty officer estimated the netting during a prewar port visit and that the same equipment remained in use. That is a proposed explanation, not a confirmed account of the intelligence collection.
Notable Point · 1:08:34-1:10:00
The uncertain source of Taranto's net-depth intelligence
The net depth was known to the planners, but the proposed explanation involving a prewar visitor remains unverified.