Something that has puzzled me for sometime is the subject of navigation when a submarine is dived. I can't imagine that a magnetic compass is all that reliable when surrounded by tons of steel, not to mention magnetic fields generated by sonar, coms etc. Astro? er no. Satnav? also no. Radio nav aids? given the piss poor propagaion of EMR underwater that sounds like a non starter. Look out on the bridge? could be something for the SBS. That leaves INAS with its attendant problems. Or is there something else?