Technical background

In the second half of the 18th century considerable advances were made in signalling technology. During this period naval warfare tactics became more sophisticated, so that more precise signalling systems were needed. Telescopes were significantly improved at this time, making it possible to signal across greater distances.

Captain Rohde´s flag telegraph, 1828. The Royal Library.

With the aid of ten different flags, pennants, etc., Rohde´s flag telegraph was able to send 1,899 different signals , helping the ships perform complicated manoeuvres. The earliest flag signalling systems on ships probably date from the middle of the 17th century. In 1743, an authorized code book was issued to the Danish Navy for the first time.

Telescope made by J. H. Smith in Copenhagen in1811, used in connection with the optical telegraph at Korsør. Post & Tele Museum.

The telescope was invented in Holland in the early 17th century. In 1757, the English optician John Dollond made a telescope, which did not break up the light in the same way as in a prism, as other telescopes did. Still, nobody was capable of making the precious telescopes in Denmark around 1800. They had to be obtained abroad.