Seneca Mills, 10 June 1863
In the winter of 1862/1863, John Mosby got Jeb Stuart’s permission to take a small cavalry command and harrass the Union troops in winter quarters in Loudoun County, Virginia. This started his career as one of the most notorious partisan rangers of the Civil War. Using speed and deception, Mosby time and again hit Federal outposts, causing some casualties, but first and foremost causing panic and distress among the Union command. Several times, cavalry detachment were sent to catch him, but despite an occasional minor success, they could not corner the swift Confederate horsemen.
On June 10, 1863, Mosby finally organised his band into an independant command as Company A, 43rd Battalion Partisan Rangers, with Mosby in the rank of a Major. Planning to conduct a raid into Maryland, he was joined by another partisan group, the Prince William County Rangers under Capt. William G. Brawner . Mosby had received intelligence that a detachment from the 6th Michigan Cavalry was encamped near Seneca Mills along the Chesapeake and Ohio Canal. He had originally planned to cross the Potomac at Rowser’s Ford at night and attack the Federals in the early dawn. As his scout got lost, the expedition did not get across the river before daybreak.
Still, his advance guard managed to capture a Federal patrol without drawing attention. When they tried to take a towboar going up the Chesapeake and Ohio Canal, they came upon another Federal patrol. Shots were exchanged, which alarmed the Michigan troops in their camp. As the retreating patrol had raised a small drawbridge over the canal, Mosby’s men were delayed and the Federals had time to saddle up. When Mosby’s men charged, they fled and retreated across Seneca Creek. While Mosby ordered his men to destroy the camp, some of them pursued the Michigan troopers, who had taken up a position on the far side of the river. Shooting from cover behind trees and brushes, their superior firepower stalled the Confederates’ attack, causing some to fall back until Mosby personally arrived. He rallied them and led them into a charge across the bridge. The Michiganders fell back again, but made another stand in a road cut. In the resulting melee, the Federals lost a flag before they finally broke and fled. In a running fight, Mosby’s men followed the Michiganders to within three miles of Poolesville .
Both sides had taken casualties. For Mosby, the loss of Capt. Brawner was especially troubling, as it was difficult to maintain command over the Prince William County Rangers without their leader. From a personal point of view, however, the raid was a success: After sending his report and the captured flag to JEB Stuart, Stuart forwarded it to Jefferson Davis with the note: “In consideration of his brilliant services, I hope the President will promote Major Mosby.” 
Capt. Charles W. Deane: Born in Vermont in 1837, he moved to Pentwater on Lake Michigan and worked there as a lawyer. In August 1862, he mustered into the 6th Michigan as Capt. of Company I. After participating in many battles with the famous Wolverine Brigade, he mustered out in January 1865. After the war, he seems to have returend to the law and for a time represented Oceana in the State Legislature. He died in 1914. 
Maj. John S. Mosby: Born in 1833, he worked as a lawyer before the war. He inlisted in the Confederate cavalry in 1861, fought in several battles and bcame a scout for Jeb Stuart. In July 1862, he was captured by Union cavalry but was soon exchanged. In January 1863, he began his operations as an independant partisan, a form of organisation that, according to the Partisan Ranger Act, allowed him to retain captured property. Derided as a “horse-thief” by the Union command, his daring raids were widely admired by the Confederates. After the war, Mosby entered politics and for a time served as consul to Hong Kong. He died in 1916. 
Capt. William G. Brawner: Born in 1832 in Prince William County, he seems to have been an influential person in his community. Working as an attorney before the war, he served as a delegate to the Virginia Secession Convention in 1861. In May 1862, he organised the Chinquapin Rangers, a partisan ranger troop in his home county. When the company was mustered in as the Prince William Partisan Rangers in September 1862, he was elected Captain. Participating in several raids and small-scale engagements, he died during the fight at Seneca Mills. 
Why did it matter?
At the time of the skirmish, the 6th Michigan was part of Major General Julius Stahel’s division, which, as part of the Corps defending Washington, had tried to catch Mosby for some time. Mosby knew of Lee’s plan to invade Pennsylvania and wanted to stir up trouble so as to pin Union troops around Washington: “it was my policy to keep up a state of alarm about the capital” . According to one author, the raid on the Union camp at Seneca Mills might even have been made directly upon Stuart’s request. Mosby’s objective would have been to scout fords to prepare for the advance of Stuart’s cavalry, which was to screen the infantry of Ewell and Longstreet. The timetable, however, was brought into disarray by the cavalry Battle of Brandy Station .
However that may have been, Mosby’s raid on the 6th Michigan’s camp indeed caused alarm in the Union command. Several units were dispatched to catch him, but none was successful. The raid cemented Mosby’s reputation among friends and foes alike as the swift and elusive “Gray Ghost”.
The most imposing landmark of the area was the Seneca aqueduct – or, more precisely, naviduct – which carried the water of the Seneca Creek over the Chesapeake and Ohio Canal and into the Potomac. There seems to have been two small bridges near the aqueduct and several mills along the Creek, which was an important source of water power.
In game terms, the canal as well as the creek count as impassable obstacles for all troops. However, as it forms the Southern border of the playing table, there is no real need to represent the canal on the tabletop. The trees and bushes along the banks of the creek block line of sight. The sunken road to the west of the creek should provide complete cover for men on horseback.
The Union Primary Deployment Point is located on the road at the western edge of the table, while the Union Secondary Deployment Point is at the camp. The Confederate Deployment Point is on the road at the eastern table edge.
This is an encounter battle. Each side has to reduce the enemy’s Force Morale to 0 while keeping its own at 3 or greater.
Camp: At least one Union group must deploy from the Union Secondary Deployment Point (camp). If this DP is taken by the enemy before a group is deployed from it, the Union automatically loses one group (so it may only deploy three groups from the Primary Deployment Point) and has to roll on the Bad Things Happen Table for Loss of Deployment Point.
Cavalry vs. skirmishers: Skirmishers (including dismounted cavalry) count as fighting without bayonets if attacked by mounted cavalry.
Union: 3 Leaders, 4 groups of the 6th Michigan Cavalry (Co. I), Support: Colour Party
Confederates: 4 Leaders, 4 groups of the 43rd Virginia Cavalry Battalion
Using Rebels and Patriots
Use Skirmishers with the unit upgrades Good Shooters and Mounted (=6 points) for the 6th Michigan and Shock Cavalry with the unit upgrade Veteran (=8 points) for the 43rd Virginia. One Union unit is deployed at the camp, the rest deploy at the site indicated as Union Primary Deployment Point.
The idea behind the scenario is a clash between two different tactical doctrines: The lightening strike of Mosby’s raiders, which relies on speed and the shock of a direct charge, versus the dismounted drill of the 6th Michigan, which relies on the firepower of repeating carbines (represented in the scenario as breech loading carbines, as those are powerful enough in Sharp Practice). The Confederate player will have to be fast and decisive, as it will be difficult to withstand the concerted fire of Union troopers in good positions.
My good friend and regular gaming partner Sigur has written a report of us playing this scenario which can be found on his blog Tabletop Stories.
 Petruzzi, David J. and Stanley, Steven A.: The Gettysburg Campaign in Numbers and Losses. El Dorado Hills: Savas Beattie 2012, p. 10-11.
 OR I: 27, part 2, p. 787-788; Scott, John: Partisan Life with Mosby. London: Sampson Low, Son, and Marston 1867, p. 99-101; Mosby, John S.: Mosby’s War Reminiscences and Stuart’s Cavalry Campaigns. Boston: Geo. A. Jones & Co. 1887, p. 157-161; Williamson, James J.: Mosby’s Rangers, a record of the operations of the Forty-third battalion of Virginia Cavalry from its organization to the surrender. New York: Ralph B. Kenyon 1896, p. 69-70.
 Wert, Jeffrey D.: Mosby’s Rangers. New York: Simon & Schuster 1990, p. 86; OR I: 27, part 2, p. 788.
 Pension records accessed via fold3.com; Hartwick, L. M. and Tuller, W. H.: Oceana county pioneers and business men of to-day, Pentwater: Pentwater News Steam Print 1890, p. 216.
 Wert, Jeffrey D.: Mosby’s Rangers. New York: Simon & Schuster 1990.
 Fortier, John B.: Story of a Regiment: The Campaigns and Personnel of the Fifteenth Virginia Cavalry, 1862-1865, M.A. thesis, College of William & Mary – Arts & Sciences 1968, p. 48 (available online)
 Mosby: Mosby’s War Reminiscences, p. 158.
 O’Neill, Robert F.: Chasing Jeb Stuart and John Mosby: The Union Cavalry in Northern Virginia from Second Manassas to Gettysburg, Jefferson: McFarland & Co. 2012, p. 211.