CONFIDENTIAL
2809. |
There is one instance on record, in which it appears the assembly required a period of two days. The time will vary, depending on the size of the submarine group - probably the larger the group, the greater their patrol area and, hence, the longer the assembly period. Concerted and repeated attacks may, therefore, be expected once a group has assembled. These attacks may be expected at night or may come in periods of low visibility during the daylight. |
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2610. |
A fair assumption is that a submarine cannot trail effectively while submerged. In any event, the submarine must surface if it is to effect the assembly of its group. Furthermore, sight, sound, or radar contact with the convoy must be maintained, even if only intermittently until the "pack" is assembled. To maintain radar contact, it must surface. To maintain sound contact, it must keep within ranges that are less than those for sight or radar contact. To maintain sight contact, it must at least show its periscope. |
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2611. |
If the convoy is of medium or high speed, the submarine definitely cannot trail submerged over protracted periods. It must frequently surface or remain on the surface and run on its engines. This, on clear days, forces upon it a minimum distance at which it must remain from the convoy while trailing. This minimum distance must be presumed to be that distance at which it cannot be seen from the nearest escort. This means that on clear days it may remain hull and conning tower down from the nearest escort, raising its periscope-for sight contact. If low visibility sets in, it is left with only radar or hydrophones as its means of maintaining contact, provided it is to remain at this distance. If radar is not used, it must close to visual distance or hydrophone distance, or both. |
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2812. |
In rough weather, the submarine must be presumed to be capable of effective trailing. In such weather, its problems increase, as do those of the screen commander's. In rough weather with low visibility, the submarine's attendant disadvantages are less than those of the screen commander's. The minimum distance at which the submarine may now trail is somewhat reduced. |
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2613. |
During darkness, the submarine has its best advantage. It can maintain sight, radar and sound contact, and still be unseen by the convoy or any escort or screening vessel. Their only means of picking it up are by radar and sound gear. The submarine will be on the surface, low in the water ready for diving. Submarines on the surface are usually difficult to pick up with sound gear. Thus, the only advantage left to the screen commander lies in properly functioning radar of the screen or other vessels. |
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