Concentration Signals

Description

By courtesy of Mr. John A. Roberts.

The concentration dials introduced in the RN in the latter part of WW1 were arranged like a clock with a short and long hand except that 12 o'clock was replaced by '0' and the remaining numbers (Roman I to IX) stopped at 9 o'clock. The hour hand indicated 1000 yard steps the minute hand 100 yard steps. There was also an arm at the back of the dial with a disc at the end which sat at the outer edge of the dial and could be aligned with number 0, II or III indicating 10000 yard steps. This arrangement covered ranges from 100 yards to 29,900 yards in 100 yard steps and was used to indicate the gun range in use. These dials were officially described in various ways including "range dial" and "clock dial" and probably quite a few others both official and unofficial. Many ships also had a second dial which was exactly like a clock (numbers I to XII, short and long hand) which was used for passing spotting information using a numeric code. The Type 31 was also employed to pass spotting and target indication information but could be used to pass other information as well (including range if necessary) — the method was (initially at least) left to the ships to employ whatever system worked best.