Cannon Ratings in Terms of Horses and Men Penetrated: How Were They Calculated?

[RJBowman]

I once saw a book, published during the second world war, with descriptions large guns (canons) used my the U.S. army and other forces.

The two fascinating things about the book:

1) Wartime censors had cut rectangular pieces out of some pages of the civilian-distributed book to preserve military secrets.

2) Canons listed in the book were rated in terms of how many horses and men the projectile could penetrate.

If I recall correctly, Verne's "From Earth to the Moon" also makes reference to canons having an estimated rating in terms of horses and men, and even makes a joke about a lack of volunteers for actual testing.

I assume that the horses and men rating must have been based on actual tests on actual retired cavalry horses, but I also can't believe that such crude testing was still being done at the dawn of the first world war. There must have been a way to measure or calculate the force of a projectile and convert that abstract mass and momentum data into the traditional horses-and-men rating. I would like to know how this was done.

Google searches aren't showing me anything. Any suggestions?

[Hurricane Annie]

 The military  were doing experiments and measures for new   technology   at least as far back as the 1800s.  The   the and horse drawn cannons were a precursor to the tank  divisions.  On contemplation, its  not out of the bounds of possibility the military. We're conducting tests and research  on the potential viability  and benefits of tanks  in the prewar  decade  and on into the war.  

 Zeppelins were being  secretly trialed accross Europe, the US and  New Zealand in the 1880s and 90s.  Hence early reports of cigar shaped UFOs

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