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![Absolute submarine harbor defense. Invented by John D. Hall, of No. 231 North Eleventh St., Philadelphia [186-].](https://cache.getarchive.net/Prod/thumb/cdn4/L3Bob3RvLzIwMTkvMDkvMTgvYWJzb2x1dGUtc3VibWFyaW5lLWhhcmJvci1kZWZlbnNlLWludmVudGVkLWJ5LWpvaG4tZC1oYWxsLW9mLW5vLTIzMS1ub3J0aC1lbGV2ZW50aC1iODRjZWUtMTAyNC5qcGc%3D/40/48/webp "Absolute submarine harbor defense. Invented by John D. Hall, of No. 231 North Eleventh St., Philadelphia [186-].")
Absolute submarine harbor defense. Invented by John D. Hall, of No. 23...
Available also through the Library of Congress web site in two forms: as facsimile page images and as full text in SGML. Printed Ephemera Collection; Portfolio 159, Folder 38.
![Absolute submarine harbor defense. Invented by John D. Hall, of No. 231 North Eleventh St., Philadelphia [186-].](https://cache.getarchive.net/Prod/thumb/cdn4/L3Bob3RvLzIwMTkvMDkvMTgvYWJzb2x1dGUtc3VibWFyaW5lLWhhcmJvci1kZWZlbnNlLWludmVudGVkLWJ5LWpvaG4tZC1oYWxsLW9mLW5vLTIzMS1ub3J0aC1lbGV2ZW50aC1lNjIyZWMtMTAyNC5qcGc%3D/40/32/webp "Absolute submarine harbor defense. Invented by John D. Hall, of No. 231 North Eleventh St., Philadelphia [186-].")
Absolute submarine harbor defense. Invented by John D. Hall, of No. 23...
Available also through the Library of Congress web site in two forms: as facsimile page images and as full text in SGML. Printed Ephemera Collection; Portfolio 159, Folder 38.