Immediately the telegraph was established successfully on land attempts were made to adapt it for submarine working. In 1845 Jacob and Watkins Brett laid a single copper wire covered with gutta-percha between England and France. This cable, which was unprotected, unfortunately broke after only one day's operation, but the feasibility of the project had been proved. A year later an armoured cable was laid at the same spot; this cable had four separately insulated solid conductors which proved to be entirely satisfactory. It was followed by T. R. Crampton with a permanent line from Dover to Calais (1851).