This device is not actually a clock for telling the time of day. It is a military tactical instrument called a range clock (or concentration dial), which was used in the era before radar to visually communicate gunnery target distances to other friendly warships in the fleet.
How it Worked
• The Problem: During the early 20th century, battleships fought in a coordinated line of battle. When firing over massive distances, gun smoke, funnel exhaust, fog, or weather conditions often completely obscured the enemy fleet from some of the ships in the line.
• The Solution: If the lead ship or another vessel in the line successfully calculated the distance to the enemy using its tall optical rangefinders, it would rotate the hands of this "clock" to display that exact distance.
• The Dial Reading: Rather than hours and minutes, the numbers on the dial represented yards or meters. Typically, the short hand indicated the range in thousands of units, while the long hand represented hundreds of units.
• Fleet Coordination: Nearby ships in the squadron could look through their binoculars, read the "time" on this clock, and instantly set their own massive guns to the correct elevation to open fire on the target without needing to visually spot the enemy themselves.
