Spotting is the process of visually observing where projectiles fired at a target fall in relation to it in terms of range (long, short, or straddling/hitting) and deflection (left, right or on). The goal in spotting is generally to prompt a spotting correction, or command to alter the range and deflection to be applied from that which would ordinarily be used on the next shot or salvo.
Spotting was generally carried out from a high platform on a mast which was sometimes called the spotting top, although quite commonly a number of additional tasks such as range-finding and target indication were performed from that platform.
Nature of Spotting
As it was often difficult to tell whether shells were long or short unless they were on the correct deflection (that is, the splashes fell along the line of bearing of the target), it was customary to seek to obtain the correct deflection through spotting before range corrections were issued. Once deflection was on, range would be brought on such that shells were seen to strike the target or fall on both sides in range and deflection. If deflection were lost, it would be immediately brought on before further corrections in range were hazarded. Spotting corrections, it should be borne in mind, were always made as an increment to be added to previously accumulated corrections and furthermore added to underlying fire control solutions being continually refined. They were, then, a feedback mechanism intended to remedy faults in the underlying fire control solution.
Difficulties in Spotting
In battle, it was generally found that shells which fell beyond a large target ("overs") could seldom be observed. Hits were often also difficult to see. Shells falling short of the target ("shorts") were the reliable observational data, and discerning whether one's battery was short, over, and on for range was often a case of counting the shorts and assuming any shells not counted were either hitting or going over.
Presumably, this also required spotters to have an idea of how many guns had fired on a given salvo, and it also implies that they needed to know when their shells were due to arrive so they could be reliably identified in cases of more than one.
Reliable spotting also necessitated that spotters and those training and laying the guns share a solid an coherent idea of what object is their target, and that they are able to keep it in sight at the time the shells fall and are to be fired, respectively. This was not always the case, and generally prompted the invention and issue of target indication systems.
A spotter also had to know when the shells of a salvo fired by his ship were due to fall so he could correctly identify his shotfall from those fired by other ships at the same target. This challenge often prompted the invention and issue of time-of-flight clocks.
Practices differed between individual ships and sometimes at the formation level for a time until a centralised policy of best practices were dictated in the form of the Spotting Rules first issued in 1916.
Curiously, though 6-power telescopes were to be permitted, spotting during prize-firing was disallowed in 1904.
The general experience drawn from spotting at Jutland was that there was no uniform and analytical method being applied to the task, and that intuition and "that seems about right" corrections were being haphazardly applied. The Spotting Rules aimed to improve and standardise the methods while simultaneously simplifying them. In this manner, the spotting system became both more confining and systematic.
At least by the British understanding of it, the American Navy emphasized selecting and training spotters who were able to judge distance of shells from their target. This, and the lack of a spotting system akin to their own Spotting Rules seemed notable to the British observers, and they commented that the Americans fully understood the British system but were not ready to consider switching to something similar.
Moreover, American conclusions seemed keenly at odds with British ones in that the American 1913 "Gunnery Instructions" emphasises the American view that single shots were easier to spot than were salvoes. The point is repeated mentioned.
- Principal Questions Dealt with by the Director of Naval Ordnance, 1904. p. 274.
- United States Navy: Proposed visit of British Naval Technical Experts. p. 22.
- Gunnery Branch, Admiralty. (1916). Spotting Rules, 1916. C.B. 272. Possibly at The National Archives. ADM 137/2028.
- U.S. Navy. (1913). Gunnery Instructions, 1913.