Moreover, when the lighthouses were inspected (following the loss of HMS Victory, which had gone down with over a thousand souls in 1744) it was found that several broken panes of glass had been replaced with wood, and that larger braziers, which Trinity House had provided to improve the lights, had not been installed (Le Cocq wishing to avoid increased expenditure on coal).

They left Les Casquets in the hands of a local agent, who recruited the keepers and managed their supplies of food and of coal for the lights.

He went on to oversee the rebuilding of the towers, which were fitted with new copper and glass lanterns containing oil lamps in place of the coal fires; these came into operation on 30 October 1779 (allowing the number of keepers on station to be reduced from seven to four).

Five years later they were again upgraded, each tower being fitted with new-style parabolic reflectors and 'a number of Argand-lamps, fixed on a ring, moving in a circular revolution, and presenting alternately a bright body of light in every direction'.

Local historian John Jacob describes the lighthouses in 1815 as being kept by 'a man, his wife and a grown up daughter, whose duty was pretty severe, in watching and trimming the lamps at night, particularly in winter, when the spray of the sea flies over, perhaps double the height of the towers'.

[7] As well as living quarters for the family, the compound contained a house for the agent to use on his visits to the island, a carpenter's shop for repairs, a small vegetable garden (with soil provided from Alderney) and a considerable amount of storage room (mostly within the two western towers), where stocks of provisions 'brought here in fair season' could be kept for winter sustenance.

Victuals such as salt beef, flour, malt and biscuit were provided by Trinity House; there were two (later three) landing areas for boats on the island, and a system of different coloured flags was used to signal to approaching vessels which (if any) was safe to use at that particular time.

[8] In 1847 a 12 cwt fog bell was added, which sounded once every five minutes in foggy weather;[5] it was placed on a small square tower near the Dungeon light, and was driven by clockwork.

Each lantern was equipped with a three-sided array of twelve 184-kilocandela lamps and reflectors, which revolved once a minute to give one slow flash every twenty seconds.

A three-sided optic with three panels on each side,[10] it was one of the first ever group-flashing lenses (newly-designed by John Hopkinson), the character of which was distinctive enough for the lights in the other two towers to be discontinued.

)[12] The new light displayed three two-second flashes every half minute;[11] it had a range of 17 nautical miles (31 km; 20 mi), at a height of 120 feet (37 m) above sea level.

The first raid, Operation Dryad, took place on 2–3 September 1942: the radio equipment was destroyed, code books were removed and the seven German keepers were taken back to England as prisoners of war.

At the same time a new optic was installed: a second-order five-panel dioptric which displayed five flashes every thirty seconds and had a range of 17 nautical miles (31 km; 20 mi).

The diaphone was decommissioned and an electric fog signal was installed on the parapet of the main tower; this, like its predecessor, produced two blasts every 60 seconds, with a nominal range of 3 nautical miles (5.6 km; 3.5 mi).