Bryan H. St. John O’Neil prepared the original guidebook for the Isles of Scilly in 1949. A (posthumous) second edition appeared in 1961, and it continued in print until at least 1971 (5th impression with amendments).
The guide was divided into sections: The Stone Age and Before; The Bronze Age; The Early Iron Age; The Roman Period; The Dark Ages; The Middle Ages; the Sixteenth Century; The Civil War; Later History. There is specific discussion of three burial chambers: Bants Carn; Innisodgen; and Porth Hellick Down.
The second edition is expanded to cover eight (rather than seven) monuments in State Guardianship. There are more plans and illustrations, including one’s for King Charles’s Castle and Cromwell’s Castle.
English Heritage has now published a volume Defending Scilly by Mark Bowden and Allan Brodie (2011). This has three main sections: Introduction; Scilly’s military heritage; Scilly and the sea. There are generous colour illustrations that cover a range of defences, not all in state care.