Lloyd consulted his expert advisors: Brigadier Sir Donald Banks, the director-general of the Petroleum Warfare Department; Sir Arthur Charles Hearn [de], a former director of the Anglo-Iranian Oil Company and the oil advisor to the Fourth Sea Lord; and George Martin Lees, an eminent geologist.[8] At the time, submarine pipelines were in use in ports and over short distances, but no pipeline had ever been laid across such a great distance or under the currents and tidal conditions found in the English Channel. Moreover, to minimise interference by the enemy and the effect of the tides, the entire pipeline would have to be laid in a single night.[6] They regarded the proposal as infeasible using any known method of construction of pipelines 6 inches (15 cm) or more in diameter.[9]