G'day everyone, Some forum members will not doubt be aware that in the late 1930's both the LNER and the LMS designed new build EMU's with air-operated sliding doors. In the 1960's BR followed their lead by introducing the class 303's (aka Blue Train units) to the Mk 1 design again with air-operated doors. Given the above, why did it take BR until the mid 1970's to start introducing other designs with sliding doors? I'm really curious to know why they did not consider sliding doors on for instance the class 304's, or the 309's and 310's etc. And for that matter all the first generation DMU's that were built. What happened on the Southern Region is hardly surprising given that they were no doubt just following what the Southern Railway had already started but none of the other designs seem to make sense. Your thoughts and contributions would be greatly appreciated! Kind regards, Richmond Commuter!