RESTRICTED 



The state of the ice should be viewed from as great a height as pos- 

 sible, preferably with glasses from the crow's nest. Not only does the 

 higher viewpoint increase the range of visibility, but it also enables 

 distant leads and open waters that are invisible from the bridge to be 

 seen. Constant attention is necessary, so that the most favorable direc- 

 tion in which to proceed can be determined by noting the presence and 

 distribution of leads or polynyas near the line of the course. Pressure 

 ridges should also be looked for so that they can be avoided and all 

 movements of the ice noted. The thickness and character of the ice 

 ahead viewed from the crow's nest may be roughly determined by 

 comparing its aspect with that of the ice already passed through, the 

 character of which is known. Arctic and Antarctic wdialers consider 

 that ice which has a greenish-blue color is the hardest and should be 

 avoided where possible. The vessel should be piloted from the bridge, 

 however, since from this point the character and thickness of the ice 

 in the innnediate vicinity of the vessel can best be ascertained. 



When the services of an airplane are available, have the plane scout 

 ahead of the vessel. By this means the nature and extent of the ice for 

 miles around can be observed, and a vessel enabled to choose the most 

 promising openings as well as those which lead in the desired direction. 

 In some instances, such an aerial survey will indicate the advisability 

 of the ship making a wide detour, skirting the pack and arriving in a 

 stretch of open water, the presence of which would otherwise have 

 been unknown. Helicopters have proved particularly useful in scout- 

 ing the ice ahead of vessels and procuring information concerning 

 leads, pools, and extent of pack. 



The ice should be carefully scrutinized from the plane at a low alti- 

 tude. Sometimes, particularly in the Arctic, pools about 6 inches deep 

 form on top of the ice. From the air and even from a distance at sea 

 level, this ice resembles open pack, but upon closer observation it is 

 found that the ice is continuous under the pools and may in fact be 

 unnavigable. Under these circumstances an erroneous report on the 

 navigability of ice may be made, resulting in considerable loss of time 

 and efficiency. It will prove helpful if aircraft observers familiarize 

 themselves with the appearance of such ice either through actual expe- 

 rience or with photographs. Observers should be employed who are 

 thoroughly familiar with the ice problems of surface vessels through 

 actual experience aboard ships working in heavy pack. The same 

 observer should be used in preliminary ice reconnaissance flights to 

 provide continuity in the picture of changing ice conditions on suc- 

 cessive flights and uniformity in the ice terminology used in the re- 



RESTRICTED 63 



