The SE&CR was not unique in employing guard’s observatories, known as "Birdcages". The SE&CR are probably the most well-known stock employing them. The SE&CR earlier shorter "Birdcages", the 50ft and 54ft sets had been well received, so the decision was made to build 60ft coaches to increase capacity. Designed by H.S. Wainwright, the Locomotive, Carriage and Wagon Superintendent of the SE&CR. At the time in 1912 these were the longest coaches running in the south of England. Renowned for their excellent riding qualities, they soon became popular with commuters. Sixty two 3 car sets were built, but after the first 30, a design change was made to the centre carriage saloon to replace one of the large windows with one smaller fixed window, and one droplight, to improve ventilation in the smoking saloon.

After nationalisation a handful of sets were converted to push-pull operation and lost their birdcages in the process. The C "Birdcages" lasted until the late 1950's in BR service before withdrawal from passenger service.

The SECR 60FT Birdcage BR Crimson for TS Marketplace includes the following coach types:

• Brake Third
  
• Brake ex-Composite
  
• Composite Lavatory (Type 1)
  
• Composite Lavatory (Type 2)