In 1596, Knyvet wrote "Defence of the Realm", full name "A breefe treatis or rather a project of a course to be taken for the defence of this realme against all forraine invasion and for the necessarie service of the same in all other actions of warre". He dated it 19th April 1596 and had it bound in red velvet for presentation to Queen Elizabeth I.
Chetham's Library have the treatise in their collection and they explain that "It was the capture of Calais by the French from the Spaniards which caused him to write the Defence of the Realm" and that his treatise laid out "His proposals for reorganizing the militia included training in the use of the long bow and the employment of archers."
You can read more about Knyvet in his biography on the History of Parliament website - http://www.historyofparliamentonline.org/volume/1558-1603/member/knyvet-henry-1537-98 and you can read copies of his "Defence of the Realm" at the following links:
- Chetham's Library digital facsimile of Knyvett MS A.4.37 - A PDF to read or download of the MS.
- Archive.org - A 1906 transcription of the treatise with introduction by Charles Hughes.