Came across the NY Met site which has loads of freebie books online (download as PDFs).

Most are on various aspects of art/design etc (from Andean Four Cornered Hats and Early American Furniture to Guitar Heroes and the Anatomical Drawings of Leonardo- and much in-between) but some are more specifically on arms/armour etc.

Link to main index is:
https://www.metmuseum.org/art/metpu...h-full-text-online?&searchtype=F&&rpp=12&pg=1

Specifically military items are:
https://www.metmuseum.org/art/metpu...of_Art?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...Swords?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...aggers?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...ection?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...nstein?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu..._Armor?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...raries?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...cional?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...1_2002?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...0_1620?Tag=&title=&author=&pt=&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpublications/Art_of_the_Samurai_Japanese_Arms_and_Armor_1156_1868

A trawl through the Met's Journal will find specific articles, such as:

https://www.metmuseum.org/art/metpu...F-D293-44E9-B972-579457F115AB}&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...F-D293-44E9-B972-579457F115AB}&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...F-D293-44E9-B972-579457F115AB}&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...F-D293-44E9-B972-579457F115AB}&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...F-D293-44E9-B972-579457F115AB}&tc=&dept=&fmt=

https://www.metmuseum.org/art/metpu...F-D293-44E9-B972-579457F115AB}&tc=&dept=&fmt=

.. and a real specialist one for those that like WW1 gear:

https://www.metmuseum.org/art/metpu...arfare?Tag=&title=&author=&pt=&tc=&dept=&fmt=

BTW: 'modern' means 1920

Very old, but some of these are interesting (free downloads from Gutenberg Press).

Lots of original references/illustrations but old fashioned text and interpretations, so treat with care!

http://www.gutenberg.org/ebooks/46342
http://www.gutenberg.org/ebooks/60767
http://www.gutenberg.org/ebooks/48573
http://www.gutenberg.org/ebooks/59209
http://www.gutenberg.org/ebooks/41676
http://www.gutenberg.org/ebooks/47878
http://www.gutenberg.org/ebooks/44538
http://www.gutenberg.org/ebooks/53092
http://www.gutenberg.org/ebooks/61751
http://www.gutenberg.org/ebooks/55439
http://www.gutenberg.org/ebooks/16273
http://www.gutenberg.org/ebooks/41617
http://www.gutenberg.org/ebooks/23186

Thanks for this site.

Rgds Victor