I came across this fascinating ebook at GoogleBooks and had to mention it here. It is a formerly confidential US Ordnance Department document entitled Handbook of Ordnance Data and dated November 15, 1918. There are photos and descriptive texts for just about every weapon system used by the US Army during WWI. Artillery, tanks, grenades, mortars, sabres, machine guns, aircraft bombs, small arms, trucks, tractors, body armor and more! There is a bit on European arms and equipment mentioned as well, for comparison purposes. Over 500 pages including the index, 226 images of equipment, 43 tables of equipment data.
P.S. - The discussion and photos of body armor developed for the trenches is very interesting in and of itself. It begins on page 413.
This is a great book, for reference material on the American Army, I am fortunate to own an original Hardback version of this book, along with others on the same subject. For any one interested in The American Army, I recommend downloading this one for your collection.
All the Best
Tim R.
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"The life given us by nature is short; but the memory of a well-spent life is eternal" -Cicero 106-43BC