The British army at Guilford Courthouse deployed for battle in a well-ordered formation. However, this order did not last very long. As the British routed the first American line, and drove into a forest to attack the second, the British regiments became scattered and disorganized. Two British units drifted so far to the right of the others that they fought what has been called a “separate battle” at Guilford Courthouse.
The two British units in the separate battle were Regiment von Bose and the 1st battalion of Guards. These two unit fought two American formations: Henry Lee’s flank corps and the “Rockbridge Rifles” .
The source material does not allow one to trace the exact movements of the units in this fight, but some generalities can be stated with confidence.
One of the most helpful accounts for understanding the course of the separate battle was composed by Charles Stedman, a British staff officer who wrote one of the first military histories of the Revolutionary War .
According to Stedman, the advancing 1st Guards found themselves facing, alone, a withering fire from a hilltop. The Guards eventually seized this position, but only to find that “another line of the Americans presented itself to view, extending far beyond the right of the guards, and inclining towards their flank, so as almost to encompass them.” The fire from in front and from the right “completed its confusion and disorder” until the battalion “was at last entirely broken.”
Stedman went on to relate that the Guards were saved by “the fortunate arrival of the regiment of Bose” which “was advancing in firm and compact order on the left of the guards...” The Hessians then wheeled to their right and attacked the Americans while the Guards rallied. The two units then made a unified drive against the Americans.
The "separate battle" at Guilford Courthouse according to Stedman (click to enlarge). The image has been cropped and red arrows drawn onto the map to clearly show the path taken by the 1st Guards and Regiment von Bose (these are indicated by faint dashed lines on the original map).
The Stedman map shows the separate battle to have been centered on a prominent hill south and west of the American third line. This hill will also be included in the Guilford Courthouse diorama I am preparing. The figure below depicts the area I am modeling (at left: the roads, fields, and topographic features that will be modeled; at right: a modern topographic map of the same area).
Below I show how the movements depicted on the Stedman map correspond with my project map. The four panels in this map represent, from left to right, four successive stages in the separate battle (note that the final phases of the separate battle are not shown). The following units are represented by numbers: 1) 1st Guards, 2) Regiment von Bose, 3) Lee’s flank corps. In the first panel, Regiment von Bose attacks the American first line, and the 1st Guards is brought up from reserve to extend the British line. In the second panel, the 1st Guards approaches a hill defended by Lee’s men. In the third panel, the 1st Guards takes the hilltop, but is driven back in disorder. In the fourth panel, Regiment von Bose wheels to the right and attacks the Americans while the 1st Guards rally.
Although the 1st Guards and Regiment von Bose had taken a key position, the separate battle was far from over. According to Stedman:
No sooner had the guards and Hessians defeated the enemy in front, than they found it necessary to return and attack another body of them [Americans] that appeared in the rear; and in this manner were they obliged to traverse the same ground in various directions, before the enemy were completely put to the rout.
The separate battle finally ended when Lieutenant-Colonel Banastre Tarleton arrived with part of the British cavalry. These troops scattered “a few hardy rifle-men” who had remained behind to harry the British.
Another valuable source on the separate battle is the journal of Samuel Houston of the Rockbridge Rifles. The Rockbridge Rifles was positioned on the extreme left of the American second line (in Brigadier-General Edward Stevens' brigade). Houston wrote that:
...the enemy appeared to us; we fired on their flank, and that brought down many of them; at which time Capt. Tedford was killed. We pursued them about forty poles [i.e., 660 feet], to the top of a hill, where they stood, and we retreated from them back to where we formed. Here we repulsed them again; and they a second time made us retreat back to our first ground, where we were deceived by a reinforcement of Hessians, whom we took for our own, and cried to them to see if they were our friends, and shouted Liberty! Liberty! and advanced up till they let off some guns; then we fired sharply on them, and made them retreat a little. 
Presumably, the “the enemy [who] appeared to us” were men of the 1st Guards, and the “Hessians” were men of Regiment von Bose.
There are two basic ways of reconciling Houston’s account with Stedman’s. One way is to assume that the events described by Houston correspond with the first set of events described by Stedman (the attack of the 1st Guards up a hill, their retreat, and subsequent relief by Regiment von Bose). The other way is to assume that the events described by Houston correspond with the second set of events described by Stedman (the appearance of an American force in the rear of the British and the subsequent round of back-and-forth combat in the woods).
As described below, neither method of reconciling the accounts is wholly satisfactory, leaving as an open question what exactly took place during the separate battle.
First, consider the possibility that the combat described by Houston took place earlier rather than later. In this case, the initial sequence of events in the separate battle might look something like this (click to enlarge):
The four panels in this map represent, from left to right, four successive stages in the separate battle (note that the final phases of the separate battle are not shown). The following units are represented by numbers: 1) 1st Guards, 2) Regiment von Bose, 3) Lee’s flank corps, 4) Rockbridge Rifles. In the first panel, Regiment von Bose attacks the American first line, and the 1st Guards is brought up from reserve to extend the British line. In the second panel, the 1st Guards attacks a hill defended by Lee’s men. The Rockbridge Rifles spy the flank of the Guards and attack it. In the third panel, fighting rages back and forth between the 1st Guards and the Rockbridge Rifles. At last, the 1st Guards is saved by the advance of Regiment von Bose. In the fourth panel, Regiment von Bose wheels to the right and attacks the Americans and the 1st Guards rally and renew the attack.
A difficulty in combining the accounts in this way is that some statements by Stedman and Houston appear to contradict.
- Stedman’s account indicates that the Guards were attacked on their right flank; Houston’s account suggests that the Guards were attacked on their left flank.
- Stedman’s account suggests that the Guards advanced on a relatively straight line, interrupted by one brief retreat. Houston’s account indicates that the fighting raged back and forth over a wide area.
- Stedman’s account suggests that the Guards were forced to retreat from a hill; Houston’s account indicates that the Guards were forced to retreat to a hill.
I tried to finesse these differences in the above figure, but the interpretation is not without problems. For example, the above figure makes it appear that Regiment von Bose was very slow in reaching the separate battle. This seems implausible in light of comments made by the British army commander, Lieutenant-General Charles Cornwallis, in his after action report:
the Hessian regiment of Bose deserves my widest praises for its discipline, alacrity, and courage, and does honor to Major Du Buy, who commands it, and who is an officer of superior merit. 
Why would Cornwallis have praised the regiment’s “alacrity” if it was slow to advance?
An alternative way of combining the accounts by Stedman and Houston is to assume that the combat described by Houston occurred relatively late in the battle (when the British discovered an American force to their rear). In this case, the initial sequence of events in the separate battle might look something like the figure below (click to enlarge).
The eight panels in this map represent, from upper left to lower right, eight successive stages in the separate battle (note that the final phases of the separate battle are not shown). The following units are represented by numbers: 1) 1st Guards, 2) Regiment von Bose, 3) Lee’s flank corps, 4) Rockbridge Rifles. In the first panel, Regiment von Bose attacks the American first line, and the 1st Guards is brought up from reserve to extend the British line. In the second panel, the 1st Guards approaches a hill defended by Lee’s men. In the third panel, the 1st Guards reach the top of the hill, only to be forced to retreat when the Americans attack their right flank. The Guards are given time to rally by the arrival of Regiment von Bose. In the fourth panel, Regiment von Bose wheels to the right and attacks the Americans. In the fifth panel, the 1st Guards renews the attack. In the sixth panel, the 1st Guards and Regiment von Bose are forced to fight off party of Americans in their rear. In the seventh panel, the 1st Guards run into a deadly fire from the Rockbridge Rifles while pursuing one group of Americans. Meanwhile, Regiment von Bose continues to fight off small parties of Americans. In the eighth panel, back and forth fighting has begun between the 1st Guards and the Rockbridge Rifles. Panels 7 and 8 correspond with the beginning of the quoted passage in Houston’s journal.
A ninth panel, were it included, would show part of Regiment von Bose advancing on the Rockbridge Rifles, as per Houston’s account. Note that in the first interpretation, the Hessians advanced on the Rifles from the west, while in this case the Hessians advanced on the Rifles from the east. I think the change in direction is a strong point of the second interpretation. It’s more plausible that the Rockbridge Rifles would have been deceived by a body of men advancing from the east – the direction from which reinforcements might be expected – than from the west – the direction from which the British originally attacked.
One cause for skepticism about this interpretation is that it is terribly complicated. Also problematic is that there is not a lot of evidence to support the fine points depicted in the figure above.
I'm not sure how I will handle the details of the separate battle when I begin representing the battle of Guilford Courthouse in miniature later this month. Feel free to leave a comment as to how you would interpret the source material.
1. Lee’s flank corps consisted of Lee’s Legion, some militia dragoons, and a corps riflemen. After the battle started, they were joined by some diehards among the North Carolina militia. The Rockbridge Rifles was a regiment of Virginia militia on the extreme left of the American second line. (See The Americans at Guilford Courthouse).
2. Charles Stedman. (1794). The History of the Origin, Progress, and Termination of the American War, Vol. 2. Note that Stedman is believed to have been at the battle of Guilford Courthouse, but it has not been established that he was an eyewitness to the separate battle. In any event, his account was probably composed years after the battle.
3. William Henry Foote (1855). Sketches of Virginia...
4. A copy of Cornwallis' report can be found in this useful compendium of primary sources.