A fine point about the functional nature of obstacles – determent value is measured in both the ability to impede and injure. You might call it a philosophical nuance, in context of the military art, but the distinction is important when considering the application of obstacle types. In practical terms, recall how the abattis and palisade were employed. These were designed, first and foremost, to slow the attackers’ forward progress, if not bar such entirely, by standing on the line of advance. Granted, if the obstruction were oriented properly and the attacker approaches with a high rate of speed, there could be injuries. An abattis is all fun and games until someone looses and eye! But even with a chevaux-de-frise, with the specified iron points, an attacker would need to do something really… well… awkward to induce a blood-letting injury. Their chief value lay in slowing or stopping the attacker just by being in the way.
On the other hand, there were obstacles that by nature were designed to draw blood. One of those was the crows-foot. Mahan described this obstacle as such:
The crows-foot is formed of four points of iron, each spike about two-and-a-half inches long, and so arranged, that when thrown on the ground one of the points will be upwards. They are a good obstacle against cavalry, but are seldom used.
Crows-foot are called caltrop among audiences which prefer Latin. Being an American, I eschew those fancy European terms where possible. Crows-foot sounds more “country.” Any rate, here’s what we are referring to:
Despite Mahan’s lack of enthusiasm for the crows-foot, the obstacle type remains in use today. The term is used to describe large concrete and steel obstacles designed to deter armored vehicles. Or on the beach to stop landing craft. To some degree it is an “offensive” obstacle… and in both senses of the word. And for emphasis here, the crows-foot doesn’t actually block movement, it injures so as to debilitate – be that a horse, a man, or, in the modern sense, a vehicle.
The downside to crows-feet was the nature of emplacement. Being sown, or basically scattered, and not pinned down, the crows-feet were not easily delineated for the defender’s convenience. An alternative was a simple field expedient:
Boards, with sharp nails driven through them, may supply the place of crows-feet. The boards are imbedded in the ground, with the sharp points projecting a little above it.
This, readers, is why soldiers need tetanus shots. Embedded in the ground, the boards could be arranged in a pattern, identified for the defender, but with the nails concealed in the dirt or surface debris. Junius Wheeler added another alternative in his post-war manual, mentioning the farmer’s harrow.
Buried upside down, the spikes of the harrow would likewise injure an unwary foot.
We don’t see many references to crows-foot or similar obstructions in the Civil War. Not to say these were not used, but rather their use was not deliberately noted. On the other hand, we see many references to small pickets with added entanglements. We should start by explaining small pickets:
Small Pickets. This obstacle consists of straight branches of tough wood cut into lengths of two-and-a-half, or three feet. They are driven into the ground, in quincunx order, about twelve inches apart, and project irregularly above it, not more than eighteen inches.
We have Figure 26 from Mahan’s manual to illustrate where the small picket might be used in the ditch:
Better yet, let us turn to Wheeler’s illustration:
The key point to latch on to here is the arrangement. Unlike the stakes in military pits, these are arranged in close order with the aim to force the attacker to think about where his foot is placed, lest the small picket pierce the foot. One might say the intent of the small picket was to discourage. But the threat behind that discouragement was that of a skewered foot. In function, the small picket was much like the punji stake from the Vietnam War:
So again we see the obstacle could be “offensive” in application. But in the Civil War context, booby-traps of this nature were not widely used. The need was for an obstacle that would stop a massed attack, not a trail patrol. So we read in many accounts of an enhancement to the small pickets:
Interlaced with cords, grape-vines, brambles, prickly shrubs, &c., they form an excellent entanglement.
And in the 1860s, engineers would add one readily available material to that list – wire. Wheeler described the arrangement as, “… made by driving stout stakes into the ground from six to eight feet apart and connecting them by stout wire twisted around the stakes.” This was an easy obstacle to set up, with materials easily obtained.
Fine point of observation here – Mahan’s entanglements were offered as a means to enhance the small pickets. Basically, the intent was to trip the attacker onto the small pickets. In Wheeler’s entanglements, which reflected wartime experience, the tripping on the wire itself was sufficient deterrent. Thus the pickets could be spread out more. An excellent description of such comes from Major Thomas Brooks in his extensive journal of operations on Morris Island in 1863:
This obstacle was made by setting stout stakes, 3½ feet long, 2 feet in the ground and 7 feet apart, in quincunx order, and in three lines. Around the top of these stakes, from 12 to 18 inches from the ground, in notches prepared to receive it, No. 12 wire was securely and tightly wound, and extended from one to the other.
Brooks reported laying 300 yards of wire entanglement on Morris Island, requiring 13 coils of wire (length unspecified) and an additional 890 feet of loose wire.
The function of Brooks’ entanglement obstacle was to deter by the threat of injury – lest the attacker be bruised and banged up from tripping. Perhaps a little nicer than Mahan’s little impaling stakes. But still an obstacle designed to injure. And of course, with the perspective of history, we recognize Brooks wire entanglement as an evolutionary step towards barbed wire of World War I and later concertina wire. In those forms, we see the obstacle designed not just to trip and bruise but to draw blood. Either way around, bruised, banged, cut, or impaled, the soldier was thus a casualty… and if lucky just placed on the disabled list.
(Citations from Dennis Hart Mahan, A Treatise on Field Fortifications, New York: John Wiley, 1852, page 48; Junius B. Wheeler, The Elements of Field Fortifications, New York: D. Van Nostrand, 1882, page 173; OR, Series I, Volume 28, Part I, Serial 46, page 304.)