YT-Y21 · Original postwar technical investigation · digitised report

Japanese 18-inch gun mounts: USNTMJ O-45(N)

Nine 46 cm guns in three triple turrets; concealed 40 cm designation; projectile weight, installed maximum elevation, reported range and firing rate; the investigators’ own evidence limits.

Author
US Naval Technical Mission to Japan
Date
February 1946
Passage
Printed pp.1–2, 5, 7, 9, 13 and 16–17 / PDF pp.3–4, 7, 9, 11, 15 and 18–19

What has been checked

Selected title, summary, references, introduction, arrangement and data pages visually inspected on 20 October 2026. Complete 62-page scan retained; SHA-256 a64aad913bc0866199c225e0404aba7c1acec2eacc08ec1613bb008d199771d4.

How to read it

Investigators had not seen a complete or operating turret. Components and interviews underpinned the reconstruction; original drawings were unavailable and some sketches were from memory. Technical figures are not independent operational trials. The armament diagram is not a certified April 1945 anti-aircraft inventory; the summary is not a complete service history.

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