UNDERWATER EXPLOSIONS 
INTRODUCTION 
Resolution of the damage problem 
4. The effect of an underwater explosion against a vessel will depend on 
both the proximity of the explosion to the vessel and the way in which the 
vessel is constructed. These effects may be sub-divided into:- 
1) the effect of contact explosions against single-hulled vessels, 
(2) the effect of non-contact explosions against vessels with some 
form of multi-bulkhead protection, 
(3) the effect of contact explosions against multi-bulkhead protected 
vessels, 
(4) the effect of non-contact explosions against single-hulled vessels. 
For case 1, a very small underwater charge is sufficient to hole a single- 
hulled vessel when in contact or near-contact and little theory is 
necessary. For case 2, however, non-contact explosions from normal types 
and sizes of charges will do little damage to a multiple protective system 
except when the outer skin is air~backed; this may be considered in the 
same way as the shell of a single-hulled vessel. Little theoretical 
treatment has yet been found possible for contact explosions in case 3. 
Therefore, the main theory to be discussed will be concerned with the 
problem of a single thickness of air-backed plating subjected to non-contact 
explosions sufficiently distant for the damaye to be appreciable, but not 
catastrophic. 
2. For such non=contact explosions the phenomena can be conveniently 
considered under the following main headings:- 
(1) The phenomena in the water which are proper to the explosion 
itself, 
(2) the interaction of these water phenomena with the target, this 
interaction depending on both target and explosion properties, 
(3) the natwre of the deformation of the target insofar as it depends 
on the properties of the target. 
3. The treatment of the material in the main text is such that a knowledge 
of mathematics beyond interpretation of simple formulae is not required. 
Where it has been thought necessary, mathematical relationships have been 
illustrated graphically. Results quoted in the main text without proof 
are deduced in Appendices and are referred to by the appropriate equation 
number. An equation prefixed by a letter is derived in the Appendix of 
that letter. 
4. The terms “open water" and "mid-water" will be used frequently. Open 
water is understood to mean the conditions which usually exist on the high 
seas where the only factors (external to the charge; which influence the 
explosion are the surrounding water and the presence oi the sea surface and 
sea bottan. Mid-water is understood to involve the further restriction 
that the point of explosion is sufficiently far from both sea surface and 
sea bottom for neither of these to exert a direct influence on the explosion. 
The most convenient explosive for underwater experimental work is T.N.7. 
and, therefore, the term 'charge' implies a charge of T.N.T. However, 
results observed for T.N.T. charges can be applied to charges of other 
explosives by means of a conversion factor. In particular, from the stand- 
point of underwater explosive effects, a 100 lb. charge of torpex is 
equivalent to 145 lb. charge of T.N.T. and the weight conversion factor of 
1-45 is reasonably constant fbr torpex charges of any size. 
