Tilt is the angle formed between the vertical of a shipboard fitting (such as a gun mounting or a director) and that of an idealized reference plane for the ship. These small imperfections in construction require corrective mechanisms for accurate gunnery.
Generally, tilt was only a problem when one instrument (such as a director) had to communicate an angular reading to another fitting (such as a gun mount) which might have a slightly different alignment. The usual remedy was to define a plane of reference for the ship and mount tilt correctors on the directors, elevation receivers and other sensitive instruments so they would "speak a common language" of elevation no matter what their angle of training.
The Royal Navy allowed gun mountings to have up to tilts of up to 20 arc minutes throughout the war, as the tilt correctors then in use could correct for this magnitude of error &mdashl in elevation. However, by the mid 1920s, the adoption of mountings of up to 40 or 45 degrees was anticipated, and while tilt correctors of the existing type could address the issue of elevation errors, the errors in training were growing and there were no cross-tilt correction systems on most sights. The deflection errors attributed to tilt would equal the tilt error at 45 degrees elevation (about 8-10 knots of deflection on most sights), and so the decision was made to reduce the maximum tilt to 5 arc minutes in 1926.
- Gunnery Branch. Addendum No. 2 to Director Firing Handbook, 1917, O. U. 6125(2), G. 10777/26, issued in September 1926.
- Admiralty, Gunnery Branch (1917). The Director Firing Handbook. O.U. 6125 (late C.B. 1259). Copy No. 322 at The National Archives. ADM 186/227.
- Admiralty, Gunnery Branch (1945). The Gunnery Pocket Book. B.R. 224/45. The National Archives. ADM 234/545.