226 § ANNUAL REPORT SMITHSONIAN INSTITUTION, 1944 
deep water generally extends reasonably close to the shore and, as is 
now known, the temperature conditions of the water are favorable for 
horizontal transmission of sound. Shore stations were used at this 
time. A shore station consists of a conventional radio receiving and 
transmitting station installed on shore, connected by electric cable with 
a submerged hydrophone placed offshore in an appropriate depth of 
water where it is not shielded by shoals. The hydrophone is attached 
to an anchor, but is buoyed to float at a selected depth below the water 
surface, 
Each shore station is manned by one or more radio technicians. The 
principal advantage of shore stations is that the radio technician can 
keep the apparatus in repair, the batteries charged, and the station 
operating at maximum efficiency at all times. Surf or other uncontrol- 
lable conditions may actuate the hydrophone if it is too sensitive. 
The radio technician can vary the sensitivity of the apparatus for the 
best reception. He can also listen to the sound of the bomb explosion 
when it is received and can measure its amplitude. A knowledge of the 
strength of the received sound is valuable to the officer in charge in 
weighting the results and in determining the size of bombs to use. 
Shore stations are more expensive to establish and maintain than 
sono-radio buoys, but their efficiency is greater. Laying the cable 
from the hydrophone through the surf to the radio station is the most 
difficult part of the establishment of a shore station, and sometimes 
weather may prevent it for several weeks at a time. And unless the 
area in the vicinity of the hydrophone has been thoroughly sounded, 
one has no assurance that intervening shoals or irregular types of 
bottom will not interfere with the receipt of the sound. 
Ship stations—When R. A. R. was first used on the Atlantic coast 
of the United States, it was soon found that shore stations would not 
function satisfactorily. The Continental Shelf on this coast generally 
extends many miles seaward, and the depths of water on it are com- 
paratively shallow. Moreover, the temperature conditions of the water 
are not so favorable for the transmission of sound as they are on the 
Pacific coast. To overcome these difficulties, small ships were anchored 
offshore at known positions and used as floating R. A. R. stations. The 
receiving stations could then be placed in deeper water, thus shortening 
the distance through which the sound had to travel. The shore appa- 
ratus was placed on the ship, and the hydrophone was anchored, as at 
a shore station, a short distance from the ship so that ship noises would 
not interfere. These ship stations were then operated just as shore 
stations. They had all the important advantages of shore stations and 
in addition they were mobile. Their maintenance, however, was ex- 
ceedingly costly, and as the ships were small, they frequently had to 
