The entrance to the harbor of Santiago, where ships of any considerable draft can navigate, is scarcely more than one hundred and twenty-five yards wide, in its narrowest places, and in order to render it hazardous for our ships to attempt to force a passage the channel was mined with both electrical and contact mines; the former of the Latimer Clark type, containing two hundred and twenty-six kilos, of gun-cotton, and the latter the Bustamente mine, containing forty-five kilos, of gun-cotton.
The electrical, or observation, mines, were planted in mid-channel, and were controlled, at first, by two stations on the west, or Socapa bank, one on Cay Smith, and one at Estrella Cove on the east bank. The station at Estrella Cove and the inner one on the Socapa bank were in the best possible positions for protection, and could have been operated even should the banks have been swept by the guns of our fleet. In the cove just behind the Morro, the operator could, in almost perfect security, observe his mine field until the ships to be destroyed were almost abeam of him, and could operate his mines long before he could be discovered.
At the Inner Socapa station the same condition of affairs existed, as the station was in behind the hill and close down near the water. Cay Smith and Outer Socapa were not so well protected, but were still commanding positions.
The length of channel controlled by these mines reached from the entrance, just off the Morro, up to about midway between Puntilla and Soldados points.
From Cay Smith across the channel, running in about an east southeasterly direction, a line of nine Bustamente, or contact, mines had been planted also, so that any ship attempting to enter the harbor would, of necessity, be compelled to pass over from eight to ten electrical mines, and then across a line of contact mines planted so closely together that she must, if of any considerable beam, surely strike one, and possibly two of them in passing.
The electrical mines were planted on the bottom in from seven to eleven fathoms of water, and the contact mines anchored to float at about eleven feet under the surface.
An effort was made to fire the five electrical mines controlled by the station at Estrella Cove when Hobson made his gallant but unsuccessful attempt to block the channel with the Alerrimac, but only two of the five detonated. Further in another mine was fired from the Inner Socapa station, and Hobson reports that it lifted the Merrimac some and probably aided to sink her, as she went down a short distance further in.
After she was sunk the defense of the channel was as follows: A line of three doubtful electrical mines controlled by the Estrella Cove station, four other electrical mines running from a point just off Santa Catalina Fort up the channel, and the nine contact mines before mentioned as running from Cay Smith across to the eastern bank; these last running just under the stern of the Merrimac. In addition to the mines the channel was blocked by two log booms running from the bow and the stern of the Merrimac over to the eastern bank, the logs being secured to each other by five-inch steel hawsers. A similar log boom was also stretched from Puntilla across to Cay Smith. (See Chart.)
The control stations for the electrical mines were small wooden huts covered with branches of trees, and absolutely concealed except for a small slit about four inches deep, and just long enough to take in the two ends of the mine field to be operated. These stations contained the most elaborate electrical appliances for testing the circuits and for firing. A large table with testing battery, Wheatstone bridge, and galvanometer was found in each, together with a firing battery, sighting quadrant, and numerous books giving full descriptions of the ships of our Navy, with photographs accompanying. All stations were in telephonic communication with each other. After the surrender it was discovered that on account of the failure of the three mines controlled by the Estrella Cove station, that station was abandoned. Only parts of the testing and firing mechanism were found there, other parts having been destroyed or carried off. The stations on Cay Smith, and Outer Socapa were also abandoned, as the inside station on the Socapa side was considered to be so advantageously located that it alone, was considered sufficient to control the remaining mines.
The means of determining the proper moment to fire the electrical mines were a sighting bar in connection with a quadrant of a circle, having on it as many contact points as there were mines in the mine field. The sighting bar was pivoted at the center of the circle from which the arc was described, and could be swung around so that its front end could be brought in contact with any one of the contact points on the arc.
The whole arrangement was evidently installed in the control station, and the mines planted on the ranges indicated by the line of sight as given by the bar in its various positions, that is, with its front end on the different contact points of the arc.
The main cable was made up of a number of small well-insulated cables, all bound together and covered with jute braiding for the distance from the control station out to the junction box, and where this cable came into the control station it was made fast, and the separate parts of it were each led to one of the contact points on the arc of the sighting quadrant. These wires, and the contact points were numbered with the same numbers that had been assigned to the mines as they were planted.
Outside of the control station the cable ran out into the water for about one hundred and fifty yards where it led into a junction box, from which branch leads radiated to each of the mines planted. The mine connection of each of these branches was as follows: In the top of the mine was a water-tight stuffing-box, through which the leading wire entered and made fast to one pole of the detonator, the other pole being made fast to the metal of the stuffing-box outside the mine. At the shore end of the cable one pole of the firing battery was placed in contact with the earth, and the other connected to the sighting-bar, the firing-key making a break between the two.
To test any particular mine, place the front end of the sighting-bar on the contact point of the arc corresponding to that mine and, with the testing key and testing battery, in connection with the Wheatstone bridge, and galvanometer, the good or bad qualities of the circuit were established. The arrangement was very simple and at the same time very complete.
To fire a mine under a vessel attempting to run the channel, connect with the firing battery, take the guard off the firing key, and, when the vessel comes on your line of sight, as indicated by the front and rear sights of the bar, press the key.
In order to make the entrance of the harbor safe for the passage of our ships the commander-in-chief, on July 17th, sent a working party in to destroy the electrical mines, and raise the contact mines. Of the four presumably good electrical mines off Inner Socapa, two failed to show continuity of circuit, and, after repeated attempts to detect their faults and to fire them, their positions were located and they were noted "to be raised." The other two were successfully fired, but the column of water thrown up by each was surprisingly small. This may be accounted for, in part, by the great depth in which they were planted.
The two noted "to be raised" were recovered in the following manner without any accident whatever: The "Suwanee," under the command of Lieutenant-Commander Delehanty, was sent in to assist in recovering these mines, as she was fitted with just the sort of anchor gear that was necessary to use in lifting them, and after the chain sling of the mine was once secured, she simply hooked her fish fall in the ring in the end of it, and with her steam winch hoisted the mine up clear of the water. All connections at the control station were broken, simply as a matter of ordinary precaution; the main cable was underrun by a dinghy for about one hundred and fifty yards, where a junction box was found. By means of a wrench the nuts holding the top on it were taken off, and the box was found to contain a branch lead from the main for each mine planted, each lead having a tag on it corresponding to its number on the contact point on the sighting quadrant. Knowing the numbers of the two mines fired, it was an easy matter to take each of the other two in turn and, leaving the junction box in a boat, underrun its cable until the end of a small chain was found stopped to it at intervals. This chain had a ring in its end, and, after casting it adrift from the cable, the boat was hauled over until it led up and down. The "Suwanee" then steamed up and hooked her fish fall in the ring in the end of the chain, hove the mine up above the water, and a steam launch went alongside and received it. A short chain sling led from each comer of the mine to a ring in the center, and to this ring the hoisting chain made fast. A vessel like the "Suwanee," or a large launch or tug with good tackles, is absolutely necessary in raising these mines, as they weigh close on to a ton and, if the bottom is soft, sink into the mud for a considerable distance.
The mines recovered were of the following general description: The case was of cast iron, about three-quarters of an inch thick, the top and body being cast separately, and, after the charge of gun-cotton had been placed inside, these were securely bolted together, with a rubber washer between them. The whole thing was in the form of an iron box about thirty-six inches on a side, and about twenty inches deep, and, as stated before, the leading wire entered through a central water-tight stuffing-box. The detonating agents were two fulminate of mercury detonators, each containing about seventy grains, as well as could be judged, connected in parallel, and embedded in the heart of the dry guncotton primer.
To prevent injury to the connections, from pulls or sudden jerks on the leading wire, a cuckold's neck was turned in it, and made fast to a ring on one of the corners of the mine. As soon as the mine was in the launch the stuffing-box was taken off to permit of an examination being made, and this should always be done if recovering a mine that has failed to fire. If the detonators have fired, well and good, if not, then remove them from the mine at once as a matter of precaution.
The remaining mine off Inner Socapa and those of the Estrella station were recovered in the same general way by the "Suwanee."
The line of contact mines, running from Cay Smith across to the eastern bank, passed just under the stern of the Merrimac and completely blocked the channel, but on the afternoon of July the second four of these mines were taken up between Cay Smith and the Merrimac, and, on the morning of July third the connections at Inner Socapa were temporarily broken so that the Spanish fleet passed out in perfect safety. After they had passed the mine fields the connections were immediately made again, and the four contact mines planted in their original places. (Chart.)
The operation of recovering these contact mines will probably be better understood after a brief explanation of the method of planting them, and a description of the different parts has been given. The description, as here given, is of the mine as it was found at Santiago, and may not be exactly technically correct according to the ideas of the inventor, but is correct regarding those recovered. The mine is in the shape of a conical buoy thirty-two inches in diameter at the top, and twelve and one-half at the bottom, and stands thirty-six inches high. It has a central axial hole in it eleven and three-quarter inches in diameter for the entrance of a cylinder containing the charge of wet gun-cotton. The bottom of this hole is closed by an iron plate, and on the outside of this plate is secured the frame of a reel which carries about twenty fathoms of wire rope for anchoring the mine. On the barrel of the reel is a toothed wheel, against which a pawl is held by a spring, preventing rotation until the pawl is raised.
On each end of the barrel, outside the frame, is a two-bladed fan, the area of each blade being about sixty square inches. When the pawl is lifted, by a rod running up alongside the mine, it releases the reel and allows the wire to unwind, and by letting go this rod the spring holds the pawl hard against the toothed wheel and stops the revolution of the reel. The fans are to prevent a too rapid revolution of the reel and a consequent snarling of the anchor wire.
The cylinder which fits in the central hole in the mine contains forty-five kilos, of gun-cotton, and is secured to the bottom plate by four bolts and nuts, but does not reach to the top of the mine by about eight inches.
In the upper end of the cylinder is a conical hole for the reception of a vessel containing the dry primer of gun-cotton. This vessel containing the dry primer is secured against a rubber washer, on the bottom of a small hollow cylindrical buoy, which fits in the upper end of the same axial hole as the large cylinder containing the wet charge.
Inside of the small hollow cylinder are six plungers, spaced at equal distances around the circumference, and converging to the center, where their inner ends rest on a glass tube filled with sulphuric acid; their outer ends being in contact with plungers operated by contact arms on the outside of the mine. The hole in the small buoy where the outer ends of the plungers make contact with those operated by the contact arms is covered with thin sheet lead to make the buoy water-tight, the blow from the contact arm being sufficient to rupture this lead when the mine is struck by a passing vessel.
Around the tube of sulphuric acid is a composition of chlorate of potash and sugar, and a central hole gives communication between this composition and the dry- gun-cotton in the conical vessel attached. To the eye, the only substances that could be absolutely determined were the chlorate of potash and the sugar, but this alone will not make, with sulphuric acid, a detonator. Therefore, there must have been some fulminate in combination with these two substances, or in the heart of the dry primer of gun-cotton, to produce a detonating effect. I quote from an opinion of the chemist at the U.S. Torpedo Station, Professor H.F. Brown. "The reaction of sulphuric acid, potassium chlorate and sugar will evolve a large amount of heat and will probably result in an explosion. This explosion will ignite dry gun-cotton, which, consequently, will produce an explosive effect. It is my opinion that this explosion will not be a true detonation unless there intervenes some fulminate of mercury, or other substance whose ignition, like that of the fulminate, amounts practically to a detonation. I should not expect the explosion of a mass of wet gun-cotton which might be adjacent to the dry primer (of gun-cotton)." This opinion is fully substantiated by other authorities, and therefore, although no fulminate appeared to the eye of the observer, it must have been there, or the mine would have been valueless. The detonating agent is, therefore, the material in the buoy and the dry gun-cotton primer.
In planting the mines the buoy and dry primer attached are placed in position in the upper end, as a last preparation, and a small rod is run across the top of the mine through lugs, to hold it in place. To one end of this rod a line is made fast, and to the end of the line a small wooden buoy is secured, intended to act as a signal buoy, the length of the line being so judged that the buoy will float a short distance under the water when the mine is planted. The buoy carrying the dry primer has a ring in its top to which a line, from the upper end of the rod operating the pawl on the reel for the anchor wire, is made fast.
The depth of water is known, as is also the depth below the surface it is intended the mine shall float. Having the mine slung, pull up on the rod operating the pawl on the reel and allow the wire to run out to the depth of water, minus the depth below the surface the mine is to float; let go the rod and lower away gently on all. The mine is pulled down under the water and floats at the depth determined upon, while the small wooden buoy, acting as a locating buoy, floats about one foot under the surface. (Sketch.)
The location of the line of contact mines was known, approximately, before the surrender, and this knowledge was verified by the commanding officer of the Spanish gunboat "Alvarado" captured in the harbor. A small boat was used in raising the mines, and the work was carried on in the early morning on account of the light and smoothness of the water, which became rough later on in the forenoon and made it difficult to locate the signal buoys. Once on the range the boat was pulled slowly, with a number of watchers on each side. As soon as one of the small wooden buoys was sighted it was secured, and by pulling on the line steadily the pin running across the top of the mine, holding the cylindrical buoy, with dry primer attached, came out, allowing the latter to rise to the surface quickly. Attached to the ring in the top of the cylindrical buoy is a line which has its lower end made fast to the rod operating the pawl on the reel for the anchor wire. Pull up on this line, lift the pawl, and allow the wire to unreel until the mine comes to the surface.
Lift the cylindrical buoy, with dry prim.er attached, in the boat, and you have nothing to deal with in the mine but a charge of forty-five kilos, of wet gun-cotton. By pulling up on the rod operating the pawl of the reel, and reaching down with a boat hook, the bight of the anchor wire was secured and the anchor weighed. A line was then made fast to the mine and it was towed .ashore and hauled up on the beach. The work of recovering eight of these mines required less than a day. This method of recovering contact mines presumes, in the beginning that their location is fairly well known, as, otherwise, the plan of sweeping for them with two boats must be carried out, as was done by the Marblehead and Dolphin at Guantanamo.
The work of sweeping for the mines at Guantanamo was done at a time when those engaged in it were likely to be subjected to the fire of Spanish riflemen in pits on the left bank of the channel leading up to Caimanera. These pits were covered by the guns of the two ships whose boats were engaged, whilst the pulling boats, in tow of the steam launches, also contained riflemen. The general plan was to sweep with the chain, and line between the boats as indicated in the sketch, and when a mine was secured, place wedges between the body of the mine and the contact arms, as a precautionary measure, until the dry primer could be taken out.
Before leaving the subject of contact mines I wish to say that I discovered an appendage to some of those recovered which I was at loss to understand. This was a small cylindrical buoy, about five inches high, and about eighteen inches in diameter, and was attached by a line to the rod operating the pawl of the reel for the anchor wire. It apparently had been intended to act as a buoy in the original design, but, as found at Santiago, there were holes punched in its sides, as though by a nail, and the result was that instead of acting as a buoy, it had an appreciable weight to it and pulled down on the rod to which it was attached, thus assisting the spring to hold the pawl on the toothed wheel. On some of the mines this was missing, and its office on those where it was found seemed to be of very little importance.
During the latter part of June a plan for countermining the channel leading into Santiago was developed and approved by the commander-in-chief; the officers who had volunteered to carry out the scheme reporting everything ready on the first of July.
The destruction of the fleet, the surrender of the Spanish army, and other incidents made it unnecessary to carry out the plan as developed, but it is simply noted here that the plan was after the accepted ideas of all nations, that is, to explode simultaneously, a number of heavy mines, containing about five hundred pounds of gun-cotton in the mine field. These mines were to have been dropped in succession from a boat, towed by a fast launch or steamer, and the whole exploded as the last mine reached the bottom. The explosion of a countermine of five hundred pounds of gun-cotton will destroy all mines within a radius of from two to three hundred feet, and the practical application of the proposed plan had every chance of success.
The mine fields were well protected by many rapid-fire and machine guns secreted on the Socapa side of the entrance; the guns and carriages being painted the same color as the earth, and almost entirely covered with brush. Between Puntilla and Cay Smith the Reina Mercedes lay in the cove, protecting the line of contact mines, whilst Punta Gorda battery could fire straight down the harbor. Added to this, the brush on each side of the entrance was thick with concealed riflemen.
Nature had done everything to assist in the protection of the channel, the electrical mines were of the most approved type, and the contact mines, if properly attended to, were dangerous to an enemy. But the very best of tools, if placed in the hands of inexperienced or indifferent workmen, will seldom give good results.
The mines in the entrance were said to have been planted by the officers of Admiral Cervera's fleet, and there were many evidences of the hurry with which they were put down. Lieutenant-Commander Delehanty, who commanded the "Suwanee," and who lifted the observation mines with his ship, says: "None of the mines were recovered intact. The connections were, as a rule, broken, the dry primers drowned out, or the mines partially exploded."
In many places the coverings of the branch cables were chafed off, and some of the strands of the wire bare; the result, no doubt, of paying the cable over the gunwale of the boat used in planting the mines.
The maxim, "that insulation is for the purpose of making electricity go where we want it to go," had evidently never occurred to the officers engaged.
In one electrical mine recovered, there was evidence of a partial explosion, which did not show at the surface of the water. The bottom of the mine was partially blown away, leaving about one-half of it intact, and inside the mine was a large quantity of wet gun-cotton, which rolled out of the hole in the bottom as the mine was lifted and lowered into the launch alongside of the "Suwanee."
In firing exercise spar torpedoes at the torpedo station, the writer has seen it frequently happen that a leak in the top of the case would admit enough water to prevent a detonation, but the case would be ruptured and the torpedo, on recovery, would show that the detonator had gone off, but that the dry primer had become damp or wet. A careful examination of the mines recovered seems to indicate that one of the small, and almost insignificant points connected with the preparation of mines had been entirely ignored. I refer to the method of securing the stuffing-box to the top of the mine. The fact that so many mines had the dry primers drowned out, together with appearance of the stuffing-box, proved that, instead of screwing down gradually on the nuts, securing the stuffing-box to the mine, so that the flange would take equally all around, one side was screwed down tight, and then an attempt was made to screw down the other side. Experience proves that this is not always possible, and I believe that this accounts in a great measure for the failure of most of the mines.
Another point was that the mines seemed to be placed too close to each other. Taking the length of channel to be guarded, and considering the fact that five hundred pound mines may be destroyed, if within three hundred feet of each other, it appears that these were too close, and the detonation of any one of them would, if it did not detonate the others next to it, at least, destroy their electrical connections and render them absolutely useless. This did happen at Estrella, and I believe also at Inner Socapa. The mines that were fired at the Merrimac utterly destroyed the connections of the three that were left at Estrella.
To get the full effect of a mine a ship must naturally be over it, but this can seldom be brought about unless two control stations are occupied. After the Merrimac sank, all but one of the stations at Santiago were abandoned, and therefore it would have been a stroke of extremely good fortune had a mine been detonated at the exact moment when a ship was over it. Experiments have, however, been made to determine the horizontal distance at which an armored vessel would be vitally injured by different charges of gun-cotton in mines, the following being the results:
10 to 15 feet
This last corresponds nearly with the conditions existing at Santiago, but with the faults in the circuits, and the other attending difficulties, it is scarcely likely that these figures would have been reached.
Contact mines of the type encountered at Santiago and Caimanera are liable, from the growth of barnacles, to become very much impaired as regards the operation of their different parts, especially the contact arms. This growth forms so rapidly in the warm water of the tropics that in a very short space of time it is sufficient to prevent the arms from driving the plungers in far enough to break the vial containing the sulphuric acid. They therefore require constant attention, and from observation it seems that, to make them effective, they should be raised and cleaned about once in three weeks. The examples of the Texas and Marblehead picking up on their screws mines of this description, are sufficient to illustrate the harmless condition to which they may revert, no matter how good they may be when planted.
Had due care been exercised in planting the electrical mines, and a fair amount of attention paid to the contact mines in Santiago harbor, no ship could have passed the two fields. But the well-known character of the people who planted and attempted to operate them accounts, in a great measure, for the condition in which they were found.
The moral effect of a mined harbor is tremendous, and the question of risking valuable ships is of vital importance. What would have happened to a ship attempting to run the mine field is problematical, but the chances were that she would have been sunk, for, notwithstanding the number of bad mines encountered, enough good ones were left to destroy her.
The electrical mine was perfect in type and design, and had it been properly planted and cared for the protection given by it to the entrance would have been absolute.
The lesson to be learned is evident:—mines cannot be planted hurriedly and carelessly, allowed to remain without attention, and then be expected to give theoretical results.
Officers of Admiral Cervera's fleet stood watch in the control stations at Santiago, and must, naturally, have been alert and attentive to their duties, so that in considering the matter from all sides the facts which come home to us are these: The theoretical knowledge of those who selected the firing stations, planted the mines, and weighed the question of properly defending the channel was fairly perfect, but in the vital point of a practical knowledge of how to prepare and plant these mines they were deficient.
It does not require much of an argument to convince us all that practical education in this particular branch of our profession is what the service needs. The details, at times so seemingly insignificant and unimportant, are just the trifles which make success or dismal failure. In a mine defense one cannot admit, for an instant, that there is a chance of failure, for it must be so perfectly installed that it may be counted upon with perfect confidence. This is feasible and possible, and a course of training would, in a short time, make the members of our service masters of the important details, without which knowledge no assured success can be expected in either mine defense or countermining.