10th Mar 2015 11:39AMThe NZMS team were fascinated by what looked to be a 10 digit clock on the ship in this image. The National Army Museum team put us in touch with Michael Wynd (research officer at the Navy Museum) who provided an explanation:

"In the pre-computer age warships needed to have a way of controlling gunnery. Warships would have a clock face with only ten numerals to assist in firing the main armament as in the example shown here fitted to USS California. Prior to the Second World War, the practice was for battleships to line up, bow to stern, and fire their guns broadside at a common target. These "clocks" were actually indicators of range. When a battleship found the range to the target, it would set its range clocks--one on the front of the superstructure and one on the aft. One hand indicated ten thousands of yards and the other hand indicated thousands of yards, so if both hands were set at 1, the clock was showing that the range to the target was 11,000 yards. Each ship would use binoculars to read its neighbour’s clock and set its clocks to match the clock of the ship which had found the range. In that manner, prior to the use of radio, the range information was silently passed down the line of ships and all ships could set their guns to fire the same distance."

Fascinating!