The following fragments have been extracted from the Admiralty Library's copy of
CB1515(20) [later OU 6171/12] The Technical History and Index (Part 20): The Development of the Gyro-Compass Prior to and During the War
1. Need for a Non-Magnetic Compass.
The large variations in the magnetic character of warships, especially after gunnery
practice or after continuing for long periods on one course, made the construction of trustworthy
deviation-tables for the magnetic compass a matter of very great difficulty. The advent of the
submarine, in which the interior of the hull is entirely shielded from the earth's magnetic field,
and in which there are very large disturbing forces due to the close proximity of powerful
electrical machinery, rendered the need for some form of non-magnetic compass still more
insistent. In 1910, therfore, when the Anschütz gyro-compass appeared, and seemed to promise
an instrument which would at all times show the true North, it naturally received immediate and
careful attention. This compass in its original form proved to be unsatisfactory when there was
any motion on the ship, for it possessed what is technically known as "Intercardinal Rolling
2. Improved Anschütz.
In 1912 the compass was redeisgned to overcome this defect and the results were on the
whole satisfactory, capital ships being fitted gradually with it....
3. The "Follow up" System.
Unlike the Sperry compass, the improved Anschütz compass does not require a follow-up
system to make it operate as such, but for the purpose of transmitting readings to repeater
compasses a follow-up system is necessary....
4. Development of the Sperry.
Early in 1913 the Anschütz gyro-compass was the only type in use in the British Navy. About the middle of 1913 the Sperry compass made its appearance on the British market, and it seemed likely to prove a serious competitor with the Anschütz. To determine the comparative value of the two types, extended trials were carried out at Greenwich in September and October 1913 with a view to settling our future policy in regard to these compasses. As a result of these trials it was proved that although the Sperry undoubtedly had "Intercardinal Rolling Error" the errors observed were no greater than in the Anschütz, the design was superior from an engineering pint of view, and practically a complete set of spares was provided at a lower cost than the Anschütz. A conference was held at the Admiralty in October 1913 which decided to mark time on the Anschütz until further trials had been carried out with the Sperry under Service conditions. As a result of the Greenwich trials the Sperry Company at once set to work to overcome the rolling error and shortly afterwards indroduced the "Floating Ballistic."
After this compass was carefully tested on the rolling and pitching table and gave satisfactory results it was generally fitted, and for some time it was thought that the trouble had been overcome, but later it was found that only in moderate weather did the "Floating Ballistic" work satisfactorily, and that in heavy seas, particularly those of a confused nature, it was unsatisfactory and caused very large errors.
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