A novel planar CTD sensor assembly is proposed for Ohio Class Ballistic Missile (SSBN), Ohio Class Guided Missile (SSGN), and Columbia Class Submarines. The sensor assembly is a form, fit, and enhanced functional replacement for the existing CTD sensor assembly. BHT’s proposed CTD sensor assembly allows for various seawater flow configurations, has virtually no latency in parameter measurement, uses on a fraction of the volume of the current seachest configuration, and uses components that have previously been qualified for DoN ship board above deck use. The planar CTD is based upon BHT’s patented technology which allows this planar CTD device to be realized