Following the successful assault on August 26, 1863 and establishment of the fifth parallel, the Federal troops encountered different sort of weapon employed by the Confederates in defense of Battery Wagner. Major Thomas Brooks recorded this entry in his journal from August 26:
On [the fifth parallel] the first torpedoes were found. One exploded, throwing a corporal of the [Third] U.S. Colored Troops, of the fatigue detail, 25 yards, and depositing him, entirely naked, with his arm resting on the plunger of another torpedo, which facts gave rise, on his being discovered next morning, to the absurd story that the enemy had tied him to the torpedo as a decoy. I was standing 20 yards from him at the time of the explosion, and Captain Walker much nearer. Both supposed that it was a shell from the enemy until late in the night, when other torpedoes were found.
As no torpedoes were recorded during the July assaults on Battery Wagner, these devices were probably setup while the Federals prepared the early parallels in late July and early August. Brooks noted the encounter with the weapon on the grounds just in front of the battery disclosed an unappreciated Confederate defensive tactic.
The discovery of these torpedoes explains what has been, to me, one of the greatest mysteries in the defense of Wagner, i.e., the fact that no material obstacle of any amount could be discovered in front of the work, not even after our two almost successful assaults. Torpedoes were the substitute.
Brooks recorded the locations of these torpedoes, with meticulous detail, on the siege line map:
I’ve pulled part of the map legend out for ease of reference, in the red box above the compass line. Oblong red “ticks” are torpedoes made from casks. The red circles are the torpedoes made from shells.
Brooks described three types of torpedoes encountered. One arrangement used a 24-pounder shell. The shell had an enlarged fuse protruding from the fuse hole. The fuse, with a ball of explosive compound on top, sat in wooden plug which reached down into the bursting charge. On top of this shell, the Confederates placed a tin box. Any pressure on the box would trigger the fuse and explode the shell. Federals uncovered thirty of these, mostly in front of the left face of Battery Wagner (looking from the Federal perspective).
Another similar type used a 15-inch shell in a similar arrangement, but with a metal fuse (see below). Brooks recorded three of this type, and speculated the shells were unexploded naval ordnance.
The most common type of torpedo was made from a ten gallon keg. On each end was a spacer, forming a float. That feature suggested the keg torpedoes were intended for use against ships instead of on land.
The Confederates buried these keg torpedoes with only the fuse sticking above ground. They laid boards over the fuses so that any weight would trigger the torpedo.
Another arrangement for the trigger was a cap with three arms, seen in the figure below:
The metal fuse, used on both the keg and 15-inch shell torpedoes, had a hollow plug as its main body. When triggered, the plunger pressed against a paper tube filled with explosive material and thus ignited the powder in the keg. When setting the torpedo, a wire threaded into the plunger prevented premature explosions.
To keep out water, a stuffing-box nut sealed off the gap between the plunger and the tube. The hollow tube threaded into a collar in the keg, with a washer sealing the gap between.
Brooks indicated Confederates planted these keg torpedoes in the area on the right, or beach, side of the approaches. With the speed of the advance, eight torpedoes were discovered inside the Federal lines on August 27. At first the Federals tried to pull the torpedoes out of the way by use of ropes. But this often set them off in uncontrolled explosions. A second method was to have sharpshooters fire on the plungers. But this was found ineffective, leaving the plungers broken but the torpedo intact. The most practical means to disarm the torpedo was by boring a hole in the wooden casing, then pouring water to render the powder inert. Brooks noted thirty were dealt with in that manner. One such disarmed torpedo appeared in the photo of the command bombproof:
However the torpedoes were also a proverbial “two edge sword.” Recall the Confederate picket line was reluctant to retreat from their rifle pits on August 26, and surrendered instead of skipping through the torpedoes. Those same torpedoes continued to hinder both attacker and defender:
These torpedoes give us considerable trouble and anxiety, but they are an excellent obstacle to prevent a sortie by the enemy, who are very much afraid of them.
All told, the Federals triggered six torpedoes and suffered a dozen casualties from the explosions. Today we would call these “improvised explosive devices.” The modern approach would involve techniques to identify the device, neutralize it, and to mitigate its effects if triggered. I’d submit the Federals did all three of those on Morris Island in August 1863. Perhaps not with the high end technology which we use today, but none-the-less effective for that time.
(Citations from OR, Series I, Volume 28, Part I, Serial 46, pages 296-7 and 310-2.)