Mechanical Aid-to-Spotter

Kilroy's Mechanical Aid-to-Spotter
This may be such a device, or an Evershed transmitter.

The Mechanical Aid-to-Spotter was designed by Lieutenant W. D. Kilroy to ensure that the spotting officer was watching the same target as was being fired upon by his own ship.

This page is not complete until I absorb the extensive data found in Manual of Gunnery for H.M. Fleet, Volume III, 1920.

Mark I

The need for this was envisioned in early 1916. It seems likely that supply commenced in late 1916 at the earliest.

The deflection dial has an index marked "S.T.Z." for "Sight Testing Zero", which is the true zero-deflection mark. The zero mark used generally is at 5 knots left deflection, meant to be an average drift deflection at all ranges. This design feature reflects the difference between turret facing and line of sight.

By 1920, it was fitted in 22 ships: Dreadnought, the three Bellerophons, Agincourt, Erin, the two surviving ships of the St. Vincent class, Neptune, the two Colossus class, the two surviving Invincible class, the two surviving Indefatigables, the four Orions, and the three surviving King George Vs.

Mark II

Supply of these to the latest capital ships commenced in the early months of 1919.

The deflection dial has an index marked "S.T.Z." for "Sight Testing Zero", which is the true zero-deflection mark. The zero mark used generally is at 6 knots left deflection, meant to be an average drift deflection at all ranges.

By 1920, it was fitted in 22 ships: the four Iron Dukes, the five Queen Elizabeths, the five Revenges, Canada, Tiger, the two surviving Lions, the two Renowns, and the two Courageous class battlecruisers.

Mark II*

This model was designed for use in light cruisers, and supply commenced in June, 1918. The great variety in gun types on light cruisers warranted removal of the "S.T.Z." mark in favor of a movable pointer that could be positioned as any given gunsight would prefer. These were not driven by Evershed racks, but from a gearbox at the director tower, immediately over the center of the director. Some worked with the Elliott Bearing Transmitter, which lacked deflection arrangement and which therefore required the Aids to Spotter to have a separate deflection box installed on the bearing transmission line.

By 1919, it was supplied to the Hawkins, Capetown, Caledon, Danae, Centaur and Birmingham classes, with plans to eventually fit it in Chatham, Weymouth, Cambrian, Caroline, Arethusa, Furious, Eagle and Hermes.

By 1920, it was fitted in 67 ships, 16 with an Elliott Bearing Transmitter and Deflection Box, and 52 with an Evershed Bearing Transmitter (details as to which are recorded on their class pages): the eight Danaes, five Hawkins class cruisers (including Vindictive), the five Capetowns, the two Emeralds (Euphrates was also listed, though she'd never be completed), the five Ceres class light cruisers, three surviving Caledons, two Centaurs, four Cambrians, two Birkenheads, two Calliopes, six Carolines, the seven surviving Arethusas, the two surviving Birminghams, six Chathams, three surviving Weymouths, Glatton, Furious, Hermes, and Eagle.

See Also

• Spotting
• Evershed Bearing Indicator
• Usborne Fall of Shot Indicator

Bibliography

• Template:BibUKFireControlInHMShips1919
• Handbook for this device (not read by me) C.B. 1285