INTRODUCTION 



In the late 1930s, Spilhaus developed the first successful instrument to measure 

 temperature continuously as a function of depth in the upper 150 m of the ocean. This 

 instrument was called a bathythermograph (BT), and the record it produced a bathytherm- 

 ogram. The instrument was widely used by the US Navy's antisubmarine forces during World 

 War II. With increased civilian and naval interest in oceanography during the post -World 

 War II years, the bathythermograph became a major instrument in acquiring information on 

 the details of the distribution of temperature in the upper 275 m of the world's oceans. 

 During this time, many hundreds of thousands of BT temperature records were acquired. 

 These records were first archived by the Naval Oceanographic Office and later by the 

 National Oceanographic Data Center. Over the years, many of these analog records were 

 digitized and presently form a major source of historical oceanic temperature data. 



In the late 1950s and early 1960s, a requirement by both the US Navy and the 

 civilian oceanographic community for an instrument that was more accurate and had a 

 greater depth capability developed. As a result of this need, the concept of a lightweight, 

 cheap, easy to use, expendable bathythermograph (XBT) was generated. By the early 

 1960s, three companies — Francis Associates, Bissett-Berman, and Packard Electric — had 

 developed expendable bathythermograph systems. 



In 1965, the US Navy organized a series of experiments to evaluate the accuracy, 

 precision, and reliability of XBTs produced in the latter half of calendar year 1964 by the 

 above three companies. The experiments were designed so a statistical analysis to compare 

 the performance of the three XBT systems could be performed. The results of these exper- 

 iments were reported by Arthur D. Little, Inc." As a result of these comparisons, the Navy 

 selected the XBT system developed by Francis Associates and manufactured by the Sippican 

 Corporation to replace the Spilhaus bathythermograph as the primary instrument to acquire 

 temperature information in the upper few hundred meters of the ocean. 



To the author's knowledge, the first operational use of the Sippican XBT system was 

 during the first half of 1966 when the Scripps Institution of Oceanography used the system 

 during the Boreas Expedition in the northern North Pacific and the Navy Electronics 

 Laboratory used the system during the FASOR II acoustic experiments conducted in the 

 northern and western North Pacific. Several hundred probes were provided to both Scripps 

 and NEL. Although few useful temperature records were obtained during either cruise, 

 several important shortcomings in the operational system were revealed. Subsequent 

 correction of these weaknesses led to the system presently in use. 



In 1966, Arthur D. Little, Inc., published a report summarizing the operational 

 characteristics and capabilities of the Sippican XBT system. They made a critical examin- 

 ation of the accuracy and precision required of environmental ocean measurements for 

 improved sonar range prediction purposes and compared these requirements with the 

 performance of the XBT system. Such items as cost effectiveness, temperature and 



Spilhaus, A.F., A Bathythermograph, /oMwa/o/yWfln>7e/?eiea/-c/i, v l,p 95-100, 1938. 

 Arthur D. Little, Iric, Experimental Evaluation of Expendable Bathythermographs, Dept of the Navy, 

 Bureau of Ships, NObsr-9305 5, Project Ser No SF-1 01 -03-21, Task 1 1353, November 1965. 

 Arthur D. Little, Inc, Expendable Bathythermograph (XBT) System Evaluation for Tactical 

 Sonar Application, Dept of the Navy, Naval Ship Systems Command, NObsr-9305 5, Project 

 SerNoSF-101-03-2I,Task 11353, August 1966. 



