The third method was suggested by Captain Torrey. It was to take the altitude of a triangle by trigonometry. A table of logarithms remaining in the possession of a naval officer, enabled us to do this. Captain Torrey laid off the base of his triangle well down in the camp, out of sight of the sentries. To measure the angle at A he described a circle on the back of a large chess-board, and divided it as accurately as he could into degrees. When the altitude B T was thus obtained, all that remained necessary to be done was to measure the distance from the base to the corner of the “shebang” (B C), and subtract it from the altitude B T. The results obtained by these two methods were substantially the same.
A great deal of earth comes out of such a hole. It was estimated that we brought out two cart loads a day. For the first day or two our plan was simply to carry it from the cabin after dark. Now this might escape notice, but if it once attracted observation, and that observation should continue from night to night, detection was certain. The boldest course is always the safest, and therefore it was determined that all the earth should be carried out in broad daylight. Accordingly a number of officers were detailed for this work. They never went for a bucket of water without filling the bucket with earth; none carried out a bag or basket empty. Little by little, the contents of the tunnel were distributed around the camp. Some was thrown in the paths and trampled down—some in the ravine, and covered with ashes, and some was used to bank up “shebangs.” It was scattered so perfectly that many of our own number were at a loss to know what had become of it.
A sentinel constantly watched the gate. When any Confederate visitor entered, a signal was given, the work stopped within the tunnel, and a blanket was spread over the shaft. Yet all these precautions did not satisfy our anxiety. The ingenious engineer of the “Diana” was again called in. He skilfully arched over the shaft, leaving a hole at one end, over which he placed the meal-box of the Hawk-eye. The bottom of this box was movable. When work was suspended in the tunnel the bag of meal and cooking utensils were thrown into the box, and it became as honest a looking box as a man could have. When work was to begin again the box was emptied, the bottom was lifted out, and there appeared a dark hole, through which a man could drop down into the shaft below.
Yet still our anxiety grew with the work. We knew that if suspicion ever fell on any “shebang” it would fall on this one. We, therefore, determined to push a sap to an inner cabin, and pass all the earth through to the less suspicious building. A wet morning gave us a pretext for digging a trench. The trench was speedily roofed and covered with earth. When fully completed, one end of it entered the shaft, and the other opened in the second “shebang.” The operation then was this: a workman in the tunnel filled a small box with earth; a second one in the shaft drew out the box, and lifted it into the “baby-jumper” (as the sap was called); a third drew it through, and emptied it in the second “shebang.”
Yet all this precaution was deemed insufficient. The “baby-jumper” was enlarged so that a man could crawl through; the box was removed, and the shaft was covered over entirely. On the very day that this was completed, the gate suddenly opened, and Colonel Allen came in. He walked rapidly to the Hawk-eye (whither he had never gone before), and contrary to his invariable custom, entered it unasked and unannounced. He saw only a bare earth floor.
It was plainly desirable that information of the projected movement should be sent to our army, and accordingly a message to that effect was duly forwarded to our lines by the Confederate authorities in the following letter:
Camp Ford, March 19, 1864,
Dear N——
“Letters came yesterday for some of• us•, and it will please J—— to know that hers did not escape this time. About a dozen of us have had letters containing news to 15th ult. There were two from mother, and one dated April 7th from C—— for me. On the whole we will not complain of our luck. I am even willing to scatter them more equally amongst the prisoners, and indeed to let others have a few of mine.
“We feel certain the blockaders at• Sabine• and Galveston keep ours. Maj. Hyllested assures us, he sent a flag off with them at least three times. Let F—— look out• for them. Some were sent in September, others in October, November and December, I think, but will not be sure as to all of these months. Those which go by Shreveport and Red River seem to get through and reach their destination in some cases.
“Stevenson (as I wrote to you) whom we left sick at Iberia, is here nearly well. Let his family know this.”
The key to this letter had been previously sent out by an exchanged prisoner. It early became apparent that secret correspondence might be useful to us and of advantage to the government. But it was necessary that it should be both secret and unsuspected. An ordinary cipher would have been as worthless as any contraband letter. My first idea was to take a certain word of every line to convey the hidden message. But this I found lengthened the letter too much, and I therefore added to these every blotted and underscored word. If a person were sure that his correspondent knew the key, and if he were allowed to coin facts and write nonsense, this correspondence would be easy enough. But it became somewhat difficult when written under the following conditions; viz., 1. To write briefly; 2. To use such words and subjects as a prisoner in that camp would naturally use; 3. To state in the body of the letter the personal information I wished to communicate; for I was never sure my key had reached my correspondent. Yet a very little practice removed much of the difficulty, and for six months, every letter carried out its twofold intelligence. If now the reader will collate the fifth word of every line, the words marked thus• and those in italics, the inner meaning of the foregoing letter will become apparent.
News now arrived of the advance of our army up the Red River. The leaves were coming out, and the time was slowly approaching when we expected to use the tunnel. The officer who had been selected to direct the work, well know that when this time should arrive it would be absolutely impossible to prevent the whole camp from talking of it, and that one careless word might ruin everything. He therefore sought to conceal the real situation of the affair, by concealing the real distance to the tree, and under-rating the amount of work actually performed. Every precaution was taken to divert attention from the progress of the work; for the inspection of the shrewd Colonel betokened that some foolish word had been overheard by the sentries, or else that we had a secret spy in camp. There were then a few straggling privates within the stockade, and suspicion pointed at two of these. A constant watch was kept upon them; and orders were given that all conversation on the subject should cease.
The night of the fifteenth of April would be the first on which the moon would rise late enough for a sufficient number of men to pass out; and on the fifteenth of April it was designed that the tunnel should be finished and the sally made. On the ninth, news arrived that a great battle had begun at Mansfield. On the tenth, rumors came, saying that the Confederate General had possessed sufficient courage to move forward and strike our invading army. On the eleventh, we heard that he had struck it in detail, routing it and driving it back toward Alexandria. On the thirteenth, Colonel Allen received orders to prepare for four thousand new prisoners. On the fifteenth, the stockade was moved back six hundred feet, and our unfortunate tunnel left high and dry in the middle of this new enclosure.