https://www.google.co.uk/maps/place/MoD+Woodbridge+-+Rock+Barracks/@52.0838414,1.3960873,676m/data=!3m1!1e3!4m7!3m6!1s0x0:0x7f5a956376e9bab0!8m2!3d52.0847806!4d1.3993835!9m1!1b1

anyway, they used to use the following....during 'submarine battery' programming....go figure: