Most of the gripper carriages were subsequently converted to electric traction in 1935. All carriages were originally built with lattice gates (instead of doors) at the ends; many were converted to air-operated sliding doors in the 1960s, but a few retained the gates until 1977. All 15 stations were built with island platforms. The trains were thus built with doors on one side only. Power for the electric lighting in the trains was supplied by two parallel wall-mounted rails (known as "T-irons") at window level on the non-platform side of the trains; trains were originally equipped with wheels to pick up the electricity but changed to skids at electrification. The trains remained cable-hauled until 1935, though the anachronistic way of supplying power for the lighting continued until 1977. The lighting circuit was also part of the operation of the signalling system. Opening times of the Glasgow subway have varied through the years, now open 06:30 to 23:40 Monday to Saturday and 10:00 to 18:12 on Sunday following a trial period between April 2011 and 2012 when the subway was open from 09:00–18:30. Glasgow Corporation took over the company in 1923 at a cost of £385,000 (). In 1935, the existing trains were converted to electric power delivered by a third rail at 600 volts, direct current. From March until December 1935, clockwise trains were cable-hauled, whilst anti-clockwise ones were electric. The conversion to electric traction cost £120,000 (). The last cable drawn car service was on 30 November 1935, and was driven by Robert Boyd. The trains lost their original plum and cream-coloured liveries, being painted red and white instead. From the 1950s the trains became all red—in a shade similar to that of London buses. During the early 1970s, trailer carriage number 41 was repainted in the original 1896 livery. According to Keith Anderson World War II brought an "unprecedented" level of use by passengers. Anderson attributes this, and an increase in patronage in the years leading up to the conflict, to the expansion of the local shipyard workforce due to the need for rearmament. Unlike its larger counterpart in London the system's stations did not make good air-raid shelters due to its much more limited depth. On 18 September 1940, during World War II, a German bomb, which dropped during a night raid on Glasgow and may have been intended for nearby naval facilities, landed on a bowling green to the south of Merkland Street station.