The first box of the GN & GE JR (the Joint March to Spalding line) as it left March was the oddly named Twenty Feet River. Located at the very northern end of March’s vast Whitemoor Yard it was a relatively new box being opened by BR in 1974 replacing the former Great Eastern box named Twenty Feet Siding that was subsiding into the soft Fenland soil. The replacement box would only be in use for eight years closing when the Joint line was shut in 1982. This spot can still be visited today as a footpath passes the sight of the box following the route of the railway into Whitemoor and forms part of the National Cycle Network's Route 63. I stood in a very similar spot in 2023 in an attempt to replicate this photograph, see….
https://www.ontheupfast.com/p/21936chg/30044473937/site-twenty-feet-river-signal-box