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sort of electrical gage with oscillographic recording. Studies made with 
various types of electrical gages demonstrated that, at least for the small 
charges being used in the new series of experiments, the gage had likewise to 
be small in physical dimensions. 
In view of the importance of the project and the necessity for de- 
vising an accurate and satisfactory gage before much real progress could be 
made on the research program, a number of different agencies began work on 
gages and carried it along simultaneously until all were satisfied that the 
desired result had been achieved. This is a case where duplication of effort, 
if it may be called by that name, was not only justifiable but necessary. 
The David Taylor Model Basin was one of the agencies which engaged 
in this program of development. This report has been prepared to give an 
outline of the history of the project and a rather complete description of 
the results as they stand to the time of writing. All of the work in ques- 
tion has been done with electrical gages; two of the final designs are of the 
piezoelectric type and one is of the electrical resistance type. 
For the convenience of the reader, the report is divided into five 
parts, giving first the general specifications for the gages, then in turn 
describing the pickup or sensitive elements and the cables and recording 
channels. The manner of calibrating the gages is described, and the report 
concludes with a description of the performance of the various designs during 
laboratory and field tests. 
PART 1. GENERAL SPECIFICATIONS 
The pressure of a shock wave resulting from the underwater detona- 
tion of a small charge of high explosive reaches its peak value in less than 
a microsecond (1 x 107° second); this peak value may be several thousand 
pounds per square inch. For explosive charges less than 1 pound, the dura- 
tion* of the pressure wave is less than 70 microseconds. The characteristics 
of a typical wave are shown in Figure 1. 
The pickup has to follow the pressure variations occurring in this 
time interval, and the period of its lowest mode of vibration must be small 
compared to the duration. For example, if this period is required to be less 
than 1/10 the duration, then the fundamental frequency of the pickup must ex- 
ceed 1.5 x 10° cycles per second. This in turn means that none of the physi- 
cal dimensions of the pickup may exceed about 1/2 inch.** The frequency 
* the duration is defined as the time required for the pressure to drop to 1/e, or 36.8 per cent of 
its peak amplitude. 
* For example, at the lowest mode a freely suspended steel disk 0.25 inch thick and 0.8 inch in diam— 
eter vibrates at a frequency of approximately 1.5 x 10> cycles per second. 
