Between 1858 and 1868 he was employed in home waters on a variety of special services, chiefly connected with gunnery, signalling and the tactical characteristics and capacities of steam warships.
In this manner Trowbridge showed that signalling might be carried on over considerable distances by electric conduction through the earth or water between places not metallically connected.
A complete system of signalling by night and day on the Morse system is worked by the police.
Many novelties, too, such as the field telegraph, balloons and signalling, were employed.
It possesses depots for artillery and mines, a meteorological observatory and a signalling station.