It could be that the book in question is only accessible in the USA because of copyright reasons, or perhaps not even scanned yet but merely catalogued by Google Books. If the former, a US member may be able to download it and email it to you, so fingers crossed! I checked Archive.org as many Google Books inaccessible via Google are available there and can be downloaded, but to no avail.
However, this may have odd useful snippets of information - US Army Field Artillery Journal Sep-Oct 1920 (it's a complete pdf link):