It should be noted here parenthetically that the term 

 "fluid dynamics" is used rather than aerodynamics , or hydro- 

 dynamics o The reason Cor this is that in the list of pro- 

 jectiles with which Division 3 was concerned were many which 

 had the first part of their travel path in air and the second 

 part in water. To insure acceptable performance such pro- 

 jectiles had to travel accurately through each of these very 

 dissimilar mediae 



Moreover, it was soon found that to regard the travel of 

 the projectile having a combined air-water path as being simply 

 divided between a period cf air travel and a 'oeriod of water 

 travel unduly simplified the problem Very frequently in such 

 cases s the transition period of water entry proved to be of 

 ~a.ior importances During this moment there are ver^ obvious 

 possibilities of mechanical damage to the projectile. Also, 

 completely apart from the damage that might be produced, the 

 fluid forces applied to the ,;rojectile during the entry period 

 might also cause it to emer 3 from the water, or charge direc- 

 tion sharply, or get out of control and assume an erratic path 

 in its subsequent underwater travelo As these facts were 

 realized, they clearly demonstrated the need for special stud- 

 ies of the dynamics of water entry. 



The first studies of projectile dynamics undertaken by 

 Division 6 were carried on oj the New London Labcrator7 r . T^ese 

 experiments were designs I ■ ■ v~ve the ^ir.hihg rate and accu- 



racy of path of depth charges. Nearly five hundred tests were 

 made in a 100 -foot training tank. 



Later, some 70C expert ents, also with scale models, were 

 conducted at the swimming pool of Massachusetts Institute of 

 Technology. The tests were aimed particularly at gaining 

 knowledge concerning the ihenomena of water entry. The models 

 were projected from an air gun and high-speed moving pictures 

 recorded the ^derwater travel. 



California Institute of Technology Contracts. 



The results of these early experiments pointed to the need 

 of a more extensive research program. Consequently, a con- 

 tract (OEMsr-207) was entered into with California Institute of 

 Technology to provide for the use of the facilities of the 

 Institute's Hydrodynamics Laboratory. 



The first research equipment constructed under this con- 

 tract was the high-speed water tunnel. The polarized light 



94 



