The District and Metropolitan Railways bought different designs of electric multiple unit. Both had open saloons; the Metropolitan trains with gated ends, the District B Stock with sliding doors in the middle of each car. When their introduction was attempted on 1 July 1905, a Metropolitan train overturned the third rail on the District Railway, requiring all Metropolitan trains to be modified before running again on the District lines. Full electric service started on 24 September, initially with 6-car trains, later reduced to 4-car. The Metropolitan trains were soon modified to enclose the gated end and eventually to add sliding doors in the middle. Trains were increased to 5 cars in 1918 and the Metropolitan introduced new stock in 1921, with three pairs of sliding double doors on trailer cars. In 1926 the Metropolitan took over all inner circle workings except for three trains on Sundays.