# How did ships acquire targets beyond the horizon in WWI?

From "The World Crisis, 1911-1928" (Winston Churchill):

... the 5th Battle Squadron had begun to fire, at the long range of 17,000 yards, upon Admiral von Hipper's last two ships.

If the horizon is about 4.7km away for an observer 5'7" (1.70m) tall, how could a ship strike a target 17,000 yards (about 15.5km) away?

• Assuming you got the distance to the horizon from Wikipedia, please read the rest of it. At 100 feet up, the sight distance to the horizon is approx 19.6km, or 21.4 thousand yards. Jan 28, 2017 at 22:02
• @CGCampbell, that's only the distance to the horizon. If the other ship also is 100 feet tall, then you'd be able to see the top of her mast from twice that distance. Jan 29, 2017 at 4:10
• "for an observer 5'7" tall" You're assuming people are standing on the sea, which seems unlikely Jan 29, 2017 at 15:35
• For those from almost everywhere on earth: 17000 yards are about 15.5 km Jan 29, 2017 at 16:57
• @jamesqf He actually just did it. Jan 30, 2017 at 9:29

Battleships were built to engage at range. Even at that time, the rangefinding gear was fairly extensive. Concerning the HMS Barham, one of the ships in the engagement:

Barham was completed with two fire-control directors fitted with 15-foot (4.6 m) rangefinders. One was mounted above the conning tower, protected by an armoured hood, and the other was in the spotting top above the tripod foremast. Each turret was also fitted with a 15-foot rangefinder.

And from the picture you can get a good idea of the height of the conning tower above decks:

For scale note the row of sailors on deck. From the rangefinders position on top of the conning tower, the visible horizon is much farther away. Scaling the diagram found on the Wikipedia page, gives a rough estimate of 120ft above the waterline. Using the formula provided here, (if my math works out), I get a range of 21.6 km, or over 23,000 yds for a minimum range. As pointed out in the comments, the other ships superstructures will project well above the waterline as well, so the actual maximum range you could visually detect another ship would vary by circumstance including the conditions and the height of the structures on the opponent vessals..

• Continuing discussions in the comment section will get the entire section removed by the moderators. Take discussions to chat. Jan 30, 2017 at 21:30
• Great idea. Ahem.... Comments are not for extended discussion; this conversation has been moved to chat.
– T.E.D.
Jan 30, 2017 at 22:23
• Those figures are maximums. In practical circumstances there is some reduction due to waves, swell, fog, spray, other vessels, surface-induced refraction and other obstacles on or near the surface about the midpoint of the range. Dec 23, 2017 at 14:12

Ships have masts. The 5th Battle Squadron was made up of ships that had lookout ("gunnery spotting") positions high enough to cater for the ranges of the guns.

The distance to horizon is approximately 3.6 sqrt(h) where h is the height of the observer in meters and the distance is in kilometers. So your 4.7 km is the distance to the horizon for a person standing on sea level. And from a 30 m tower the distance is 20 km.

Here is a scale diagram of Warspite in 1918 from this post on World of Warships (only minor modifications were incorporated since Jutland so in tems of rangefinder heights this is representative). From this drawing we can take measurements, which gives the height of the rangefinder above the fire control top on the foremast is about 28m above the top edge of the boot topping (the black band around the hull approximately where the waterline would be). So the height above the water line in combat should have been within a meter or so of 28m.

This would put the geometric horizon at about 19+ km (~21 kyd). So the maximum range at which an opponent could be seen by the range finder would be maybe something like 35 km (~ 38 kyd).

But this is academic for Jutland as visibility was constrained by the weather conditions and the smoke not by the geometric horizon.

(also note the refraction will result in the horizon generally being further away than the geometrical horizon)

Added for information, the longest range hit by one underway warship on another is a toss up between Warspite's hit on Guilio Cesare during the Action off Calabria (the battle of Punta Stilo) July 1940 at ~26 kyds, and Scharnhorst on Glorious in June 1940 at about 26.2-26.5 kyds. The uncertainties in the figures make it difficult to say that the latter was definitely at a longer range than the former.

• When it comes to abusing mixed units I think kyds should get a medal Jan 31, 2017 at 9:32
• @Separatrix you must be living a sheltered life if you have not seen kyds and more bizarre units in your working life. The use of kyds is a convenient way of reducing the number of zeros when typing. Perhaps you should be more concerned with the terrifying kslug. Feb 1, 2017 at 5:18
• It's a unit that says "I accept that metric is better in every way but I'm still not going to use it". I recommend The Register's unit converter so you can give distances in London buses. Feb 1, 2017 at 13:42
• I do think SI units are better in every way. But historically we should stick with contemporary units (of course we could pretend to be discussing this from the German point of view and use metres). Also when working for a defence contractor one is obliged to use the units mandate by our customers however absurd. Feb 2, 2017 at 7:58
• My favourite is the speed of light in furlongs per fortnight: 1.802 * 10^12. Dec 23, 2017 at 14:20

A couple ways:

1. As several others have stated: the horizon gets farther away the higher you are, so putting lookouts on top of masts lets them see farther. Also, it works in reverse, so it's possible to see tall things (like the masts of other ships) from farther away.
2. Spotters. Like any other artillery, they could use of forward spotters to locate the enemy and report on accuracy of fired shots. On the sea, these spotters could be small boats or planes which could report via radio.
• Spotters!? The triangulation effort for three objects moving in different, rapidly changing, directions at speeds in excess of 20 knots would require computational efforts vastly above anything available in World War Two. This isn't like stationary howitzers firing at stationary targets guided by stationary spotters. The logistical efforts to launch and retrieve those small boats would be prohibitively dangerous to the mother ship, because of having to slow down while doing so. I could go on. Dec 23, 2017 at 14:36
• Dec 23, 2017 at 14:39