The "D" type cars were the least common of the car types; only 18 cars were fitted with control equipment and coded "D" by 1923. The rest were known as "ringer" trailers, having a white ring on the door indicating the compartment was available for the use of passengers. These cars were paired with M cars and run either in pairs, i.e. M-D-M-D replacing an M-T-T-M set, or in some cases M-T-D sets ran on particularly flat, short-distance lines where late running, while annoying to the passengers, would not disrupt the entire system. One such example as the Altona Beach to Newport shuttle service, running hourly as of 1939.