The Maunsell High Window stock was initially authorised in 1929 by the Southern Railway. The BTK stock was built to Order No. E707, under diagram D2110, with thirty vehicles entering service in September 1933, whilst the FK stock were built to Order No. E490 and delivered in August 1930. Comprising sixteen vehicles under diagram D2501, they originally formed part of eleven coach trains for the Waterloo-Southampton services. The TK stock was built to Order No. E705, a large order of fifty vehicles to diagram D2001 that was delivered in December 1933.