47 
123. At distances greater than the critical distance, the first bubble 
pulse originates from a source away from the target and its interaction 
with the target can be treated along the lines indicated for the pressure 
pulse in para. 102-113. The main point to be noted is that the bubble 
pulse is fairly long compared with both the target plate and baffle 
dimensions. The discussion concerning long pulses is thus especially 
relevant to the bubble pulse in thess box model experiments and diffraction 
effects lead to a transferred energy some two to four times the energy 
in the part of the bubble pulse directly incident on the target plata 
12h. Summing up, in small-scale experiments with box or drum models both 
the attraction of the bubble to the target and diffraction effects enhance 
the importance of the bubble which can produce damage comparable with that 
due to the initial pressure pulses The relative importance of the bubble 
is greatest when the charge is a certain critical distance from the 
target corresponding to the bubble arriving at the target when it is of 
minimum radius and the resulting bubble demage tends to be concentrated 
locally on the target plate. 
125. For actual ship targets the importance of the bubble in causing 
damage is much more problematical, For small charges fairly close to a 
target vessel it seems likely that the bubble can contribute appreciably 
to damage; this is relevant to the attack of submarines by a large 
number of small charges (one of which may explode close to the target) 
rather than one large chargee On the other hand, for large charges the 
movement of the bubble towards the target will in general be small, this 
movement increasing much slower than the scale of the explosion, and it is 
doubtful whether bubble damage is of importance for such full-scale 
non-contact charges against single-hulled vessels, A possible exception 
is the enhanced effect already mentioned for charges directly beneath 
the ship's bottom, this effect depending primarily on the rise of the 
bubble dus to gravity though it may be assisted by the target attraction 
as the bubble approaches the ship's bottom. 
