The distinction between a coast-defense and a harbor-defense submarine lies in the former's greater submerged and surface endurance, greater speed, and superior habitability. All submarines in our service not classed as harbor-defense boats may be regarded as coast-defense submarines. Taking our "D" boats as the most inferior of this class, we find that they have a demonstrated radius of about 1,000 miles and are self-sustaining for a period of about 10 days. Their submerged radius is 35 miles at 8 knots and about 75 miles at 5 knots. Their torpedo armament consists of four 18-inch tubes in the bow capable of taking any 18-inch torpedo now in service.
In considering the tactics of coast-defense submarines it is assumed that they would be concentrated in groups at certain bases on the coast. On information from shore stations or scouts that the enemy has appeared approaching our coast, the group or groups nearest would proceed to intercept, using highest reliable surface speed (10 knots for "D" class and about 11 knots for "E" class).
Cruising formation should be column, distance 1,000 yards. Boats should be in awash condition with radio up to intercept any information that may be sent broadcast or directly to them.
On sighting the smoke, boats should submerge and take further observations only through the periscope. The problem that confronts the group commander is to bring his group into contact with the enemy and within torpedo range at the same time. To insure this, individual boats must conform to the general movement, and as signals will be impracticable when near the enemy column "follow-the-leader" tactics appears the only practicable method of insuring coordination. Once within maximum torpedo range the group should be on the bow of the enemy formation. If the distance is 1,000 yards, each boat can attack without risk of collision with neighboring boats, when it judges that the moment has arrived.
The proper bearings on which to fire torpedoes with the maximum chance of hits against an enemy in any formation is the same as for surface boats and has been considered by the Naval War College under the section devoted to destroyers.
As in the case of harbor-defense submarines, boats that have exhausted their means of offense should proceed with the same precautions to the designated base.
Should the attacking group discover the enemy at anchor, landing troops, or establishing a base, and with submarine defense yet unprepared, the attack might be much simplified. The enemy's patrol and pickets could probably be passed at night, and the most serious obstacles to success would be nets and mines with which the enemy would
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We searched the National Archives Catalog and located the Logbooks of U.S. Navy Ships, 1801 - 1940 in the Records of the Bureau of Naval Personnel (Record Group 24) that include the deck logs of USS D-1, USS D-2 and USS D-3 for September and October 1917. We also located War Diaries, 1919 - 1927 (documenting 4/1917 - 3/1927) in the Naval Records Collection of the Office of Naval Records and Library (Record Group 45) that may include war diaries for these vessels. For more information, please contact the National Archives in Washington DC - Textual Reference (RDT1) via email at email@example.com.
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