In late November 1923, with Heck aboard, Guide began a voyage from New London via Puerto Rico and the Panama Canal to San Diego, California, where she would be based in the future, with her route planned to take her over a wide variety of ocean depths so that she could continue to test her echo sounder. Guide made history during the voyage, becoming the first Coast and Geodetic Survey ship to use echo sounding to measure and record the depth of the sea at points along her course; she also measured water temperatures and took water samples so that the Scripps Institution for Biological Research (now the Scripps Institution of Oceanography) at La Jolla, California, could measure salinity levels. She also compared echo sounder soundings with those made by lead lines, discovering that using a single speed of sound through water, as had been the previous practice by those conducting echo sounding experiments, yielded acoustic depth-finding results that did not match the depths found by lead lines. Before she reached San Diego in December 1923, she had accumulated much data beneficial to the study of the movement of sound waves through water and measuring their velocity under varying conditions of salinity, density, and temperature, information essential both to depth-finding and radio acoustic ranging.
