Long range sound transmission : interim report no. 2, SOFAR bombs and detonators

Abstract

The use of the natural sound channel in the oceans in transmitting sound signals over distances as great as 3000 miles is known as SOFAR. The sound signal is initiated at the axis of the sound channel by some sort of bomb and the signal so generated is picked up at great distance by a hydrophone lying at or near the axis of the channel. It is the purpose of this paper to discuss the design and performance of the bombs developed to date for use in SOFAR. The bombs fall into two general classes, namely explosion bombs and implosion bombs. Explosion bombs consist of a detonator which by means of a booster fires a main charge usually of TNT or other high explosive. The only practical method of actuating the detonator at the present time is on the basis of pressure, the detonator being designed to fire at a pressure corresponding to that at the sound channel axis. As the depth of the axis varies with the geographical location it is necessary that the detonator be replaceable or that it be adjustable to meet the requirements of a given area. Typical firing depth requirements to be met are 100 fathoms in the temperate latitudes in tho Atlantic and 350 fathoms in corresponding latitudes in the Pacific. Explosion bombs have varied in design from uncased demolition blocks fired by a simple dotonator to a cast charge of TNT in a pressure proof case fired by an intricate mechanism with elaborate safety devices. Detonators have been principally of three types; (1) the Woods Hole pressure detonator, (2) the diaphram-percussion pin, and (3) the bourdon-electric. Implosion bombs consist of empty containers designed to collapse at or near the axis of the sound channel and thus to release sound energy. It is not know how efficient this sound source is as development work on it has been somewhat limited. The advantages of this device is that it is perfectly safe to use under all conditions, and that it is simple to manufacture. The main disadvantage is that it is rather bulky.