With the development of any new weapon of war the first reaction is an exaggerated estimate of its invincibility. This is usually followed by the development of countermeasures, which in turn are credited with almost fabulous powers of destruction. It was so with the submarine and the depth charge in the World War. At first it seemed hopeless to try to combat the submarine. Then came the depth charge, and opinion veered to the opposite extreme. It was popularly supposed that the explosion of one of these anywhere in the vicinity of a submarine would cause the submarine to crumple up. A more accurate estimate of the destructive effect is given by Admiral Jellicoe in The Crisis of the Naval War; within 14 feet it will destroy the submarine, within 28 feet it will disable it, and within 60 feet it will have a demoralizing effect. In the case of an experienced and well-disciplined crew, this demoralizing effect is probably very limited. There are numerous records of German submarines which underwent repeated bombardments at fairly close range, but which nevertheless continued to operate effectively. However, there is no doubt that in many cases it had the effect of deterring a submarine from pressing home an attack when it was in a position to do so. The success of the convoy system may be largely credited to this effect.
The first reported use of depth charges against submarines was made on July 20, 1915, when the British armed trawlers Quickly and Gunner made an unsuccessful attack on a German submarine. The first successful depth charge attack was made a year later on July 6, 1916, when the British motor boat Salmon sank the UC-7. The Salmon used hydrophones to locate the submarine and dropped only one charge, which apparently detonated the mines in the UC-7's mine chutes. It was not until almost a year later, in May, 1917, that the Germans learned of the existence of the new anti-submarine weapon.
Prior to the entrance of the United States into the war, our Navy had developed a depth charge containing only 50 pounds of explosive. Upon our joining the Allies this was perceived to be ineffective, and the charge was increased to 300 pounds, the same as the British depth charge, and this was the standard weight used throughout the war. In September, 1918, a 600-pound charge was issued, but it does not appear that any were actually used. They would undoubtedly have increased the radius of effectiveness, but by just how much it is impossible to determine.
Prior to the Armistice over 38,000 of the 300- and 600-pound depth charges had been delivered to the United States Navy. Assuming that half were expended, we have 19,000 as the number used. From figures given in The Submarine War, by Gibson and Prendergast, we may assume that the British Navy expended at least as many. Thus, taking into consideration those expended by other allied navies, more than 38,000 depth charges were expended. A total of 38 submarines were sunk by this means, giving an average expenditure of over 1,000 depth charges for each submarine sunk.
The submarine will undoubtedly be an important factor in any naval war of the future, and the depth charge will probably again be the principal weapon against it. It is pertinent, therefore, to study the effect of the depth charge on the submarine, particularly with a view to determining the actual damage done and what measures may be taken to render the submarine less vulnerable.
The accounts of the sinking or damaging of various submarines given by the interrogation of survivors or by the submarines’ war diaries show that in many cases the damage was of a minor nature, that is, it might have been obviated by improved design, could have been repaired at leisure had not the presence of the enemy prevented surfacing, or the depth of water precluded bottoming.
The answer to the depth charge from the submarine’s point of view is greater ruggedness and resistance to shock in the depth regulating mechanisms, protection of the batteries and motors from entering water, and protection of the personnel from gas. This, of course, may be met by an increase in the weight of the depth charge. However, even with heavier charges, submarines can probably be developed to survive any explosion except such as cause actual ruptures of the pressure hull.
The following case histories throw some light on this subject.
“UC-26” sunk in the English Channel, May 9, 1917.—This case is interesting to study in regard to depth charge effect, although the primary cause of her loss was ramming, a depth charge being secondary. It also illustrates an interesting point in connection with escape from a sunken submarine.
The UC-26 was sighted at 0100 by three British destroyers, and on account of her slowness in diving she was rammed by H.M.S. Milne just forward of the conning tower. Water entered, but not very rapidly, and no gas was noticed. She sank to the bottom in 150 feet of water. Soon afterward a depth charge exploded nearby, extinguishing all the lights. An effort was made to blow tanks and come to the surface, but the attempt failed. Whether this failure was due to the damage caused by the ramming or the depth charge was not determined. The water rose inside the boat, and the crew turned to efforts at escape. Attempts were made to open a hatch, but the pressure of water outside prevented. The captain then said, “It is no good,” and ordered three cheers for the Kaiser, which were duly given. A petty officer meanwhile had the more practical idea of turning on compressed air into the compartment. This soon raised the pressure inside to equal that outside, and the hatch was opened without difficulty. A number of the crew managed to get out and reach the surface, but only two survived, both of whom had ascended slowly. The death of the others from excessive air pressure in their lungs was probably caused by too rapid an ascent or too slow' venting of the air in their lungs.
“U-58” sunk off the southern coast of Ireland by the U.S.S. “Fanning,” November 17, 1917.—The submarine was making an approach on a convoy to fire a torpedo. The Fanning dropped only one depth charge, slightly ahead of the estimated position of the submarine. This charge exploded near the stern of the U-58, which was submerging at the time. At first there appeared to be no damage, but after a few minutes the motor controlling the horizontal rudders blew out, either from shock or from entering water. While endeavoring to control the depth the boat went down to a depth given variously as 130-250 feet, then came up near the surface and went down again to 278 feet.
By this time entering water seems to have got into the batteries and caused the generation of gas. There is some confusion as to whether or not water actually entered the boat, some of the survivors denying it, and one stating that if the water had been sufficiently shallow they would have lain on the bottom and made repairs. At any rate, the captain decided at this point to come up and surrender, and he blew the tanks. On the way up the motor con trolling the vertical rudder blew out. On reaching the surface the submarine was met by another depth charge, dropped by the U.S.S. Nicholson at a distance of 10 feet. Fire was opened on the submarine by the Fanning and Nicholson, until signs of surrender were made. No hits were made by the gunfire. The Fanning rescued the crew, and the submarine sank with her hatches open, as a result of explosive charges placed by her crew.
"UC-38" sunk in the Aegean Sea by French destroyers "Lansquenet" and "Mameluk," December 14, 1917.—At 8:05 A.M. the submarine torpedoed the French cruiser, Chateaurenault. At 8:55, she fired another torpedo at the cruiser, and was attacked with depth charges by the two escorting destroyers. The propellers of the destroyers were heard passing overhead. The explosion stopped all clocks on board the submarine, but at first there seemed to be no serious damage. The torpedo-leading hatch in the motor-room was seen to be leaking, the explosion having buckled a part of the hatch cover. Water fell on one of the motors and soon short circuited it. The pump was set to work to rid the boat of the water, but it soon stopped working, and the auxiliary pump was started but proved inadequate. Another depth charge exploded, which did no damage except to extinguish the lights, which were replaced by the emergency lights.
The submarine was proceeding dead slow on one motor. In consequence of the water entering aft, the boat lost her trim, and was down by the stern at a steep angle. The crew were ordered forward to help restore the trim, but this caused the water to wash over the motors, putting the second one out of commission.
To this situation, the commanding officer decided that there was nothing to do but blow ballast tanks and come to the surface. On reaching the surface, the boat was fired on by the destroyers and sank while the crew were abandoning ship. Eight of the crew were lost.
“U-110” sunk off the northwest coast of Ireland by E.M.S. “Michael,” March 15, 1918.—The submarine had just torpedoed the SS. Amazon when she sighted a destroyer on the horizon and dived to 130 feet, remaining at that depth for about 30 minutes, when several depth charges exploded near by. The boat was violently shaken, and the diving rudder motor put out of commission.
The hand gear was thrown in, but not in time to prevent losing trim and diving to 334 feet. The pressure of the water forced a stream through the studs which connected the water pump discharge pipe to the hull. The crew were ordered aft to help restore the trim, the tanks were blown, and she rose rapidly to the surface. Another attempt was made to dive, but the depth could not be controlled. The captain then brought her to the surface, and as two destroyers were sighted three miles away, approaching at full speed, he ordered all hands on deck in life jackets, and when fire was opened on her by the destroyers, the crew gave three cheers for the Kaiser and jumped overboard. Arrangements had been made to sink her, but she sank under gunfire. There were nine survivors.
“U-104” sunk off the southeast coast of Ireland by H.M.S. Jessamine, April 25, 1918.—The Jessamine sighted the submarine on the surface and headed for her at full speed. The U-104 made a quick dive, and had reached 98 feet when the first depth charge exploded, forcing the bow up, but doing no damage. The second depth charge forced the stern down and admitted water into the motor-room. A third depth charge exploded, and an attempt was made to blow all ballast tanks, but because of the damage to the after tanks only the forward tanks could be blown. This caused the bow to rise still more, the depth gauge forward showing 33 feet. The men in the forward compartment seized this opportunity to escape, and opened the torpedo hatch. Only one man escaped.
“U-108'’ depth charged and damaged by U.S.S. “Porter,” in the western approaches to the English Channel, April 28,1918.— The submarine was heading to attack a convoy when its periscope was sighted by the Porter at about 1,000 yards. The Porter arrived at a point about 30 yards directly astern of the submarine before it submerged. When the stem of the Porter arrived at a point about 20 yards ahead of point of submergence 2 depth charges were released from the stem, followed 6 seconds later by 2 from the throwers, and at 10-second intervals by 19 single charges, 23 in all, set for 150 feet. The submarine dived quickly, and had reached a depth of 200 feet when the first depth charges exploded. The first three charges threw out the automatic devices on the after battery and put out of commission all the order transmitting devices, the alarm gongs, and the conning tower wheel. The trimming pump functioned at first and then failed. Additional damages not discovered at the time were the flooding of the after torpedo tank due to rupture of the upper pipe; the breakage of the glass in a manometer tube; the failure of a blank flange fitted by the ship’s force three days before; and the flooding of the port displacement tank, which could not be drained. The boat then went down to 230 feet, and took a trim by the stem of from 10 to 14 degrees, and could only be held from a greater trim by going ahead at high speed. The submarine continued sinking to 300 feet. At this depth the boat started to make water in the forward compartments, and occasional crackling was heard in the rivets. A litmus test revealed acid in the bilge water, although no gas was reported at any time.
Continuous efforts were made to regulate depth and trim, but without success. The boat moved up and down erratically, and at one time struck bottom at 330 feet, with a trim of 45 degrees by the head.
At 11:00 p.m., the boat came to the surface to charge batteries and air flasks. It was found that they were floating in a huge lake of oil, evidently from a leaking oil tank. At 11:30 P.M., a quick dive was made to avoid a destroyer about 800 meters distant. At 12:05 a.m., the submarine was again brought to the surface, where she remained the rest of the night.
It was then decided that the damage was such as to interfere with the proper maneuvering of the boat, and she returned to her base immediately. The U-108 was on her first cruise, and this interruption came before she had achieved any results.
After the Armistice the U-108 was assigned to France, and is now the Leon Mignot.
"UB-72" torpedoed and sunk in the English Channel by British submarine "D-4", May 12, 1918.—Her case is interesting, as an example of the amount of punishment a submarine can stand from depth charges. On May 7 and 8 a total of 51 depth charges were dropped on UB-72. The first three were from a dirigible, and apparently caused no damage. Next, she was pursued for two hours by a destroyer which dropped 23 depth charges, opening up a leak in an oil tank and causing her to leave a track of oil in her wake. Next day the submarine was again trailed by a destroyer, which dropped 20 depth charges, shaking up the boat considerably, and extinguishing 5 lights. Later in the day, a patrol boat dropped 5 more charges on her. She proceeded and patrolled without further incident until she was torpedoed on May 12.
"U-64"sunk in the Mediterranean by H.M.S. "Lychnis," June 17, 1918.—The first depth charge jammed the vertical rudder, and probably the after diving rudder, and extinguished the starboard lights. The explosion forced a momentary opening in the forward hatch, and a small amount of water entered before the water pressure again sealed the hatch. The commanding officer gave orders to dive to 100 feet at full speed, but as the boat was down by the stern her bow was forced up and she broke surface. Again she dived, and again broke surface, when it was learned that the after trimming tank was damaged, and that she was making water both forward and aft. The tanks were then blown and the boat brought up with the intention of escaping on the surface. When she reached the surface, a hot fire was opened by three ships present, and the submarine sank. There were five survivors.
"UB-110" sunk off the east coast of England by H.M.S. "Garry" and M .L. "263," July 19, 1918.—The first depth charge exploded underneath the submarine, forcing her up, and jamming the forward diving rudder in the up position. Another depth charge exploded aft, short-circuited the port main motor, and damaged a fuel tank. The submarine came to the surface in spite of efforts to dive, and she was rammed, fired on, and rammed again, whereupon she sank. There were thirteen survivors.
This submarine was later salvaged by the British. Her log showed that she had been depth charged on each of the twelve days preceding her sinking.
“UB-124” sunk off northeast coast of Ireland, July 20, 1918.—This submarine had just torpedoed the British transport Justicia, and on account of delay in compensating for the weight of the torpedoes, she broke surface, and was attacked by British destroyers with depth charges. In the excitement of the explosions, the trim was lost, and the boat dived to the bottom, 282 feet, where the captain decided to remain. During the next hour and a half, about 50 depth charges were dropped in the vicinity and an hour later 5 more. Four hours later, at dusk, the tanks were blown, and the boat ventured to the surface. In rising, the boat took an inclination of 50 degrees by the stern, as a result of damage to one of the after tanks or by failure of its blow valve. Acid ran out of the batteries and mixed with the sea water, generating gas. The destroyers were seen approaching from about 5 miles away. Escape being impossible, all hands were ordered on deck, and the boat was sunk with demolition charges.