Walter Brooke Cox joined the army, like many other men at the time, with the hope of making a name for himself.
Commissioned on January 3, 1776 as a cadet, Cox joined Captain Patrick Sim’s Second Company of the First Maryland Regiment.  Under Captain Sim’s guidance, Cox’s first engagement with the British occurred during the Battle of Brooklyn on August 27, 1776. During the battle, the Continental Army attempted to defend itself New York from the British. However, the British Army outflanked the Americans.
As they retreated, Sim’s company was ambushed by a platoon of British soldiers. However, “fighting with more than Roman courage,” the First Maryland Regiment forced the British back, allowing Scott and his company to escape across Gowanus Creek to the fortified American lines, while other companies were forced to travel up stream. Those companies ultimately confronted and fought another British platoon. These charges by the Marylanders and the bravery they showed earned them the title of the “Maryland 400.”
Like the soldiers featured in past posts, Cox subsequently fought in the Battle of White Plains, where the Americans once again suffered a debilitating defeat.
In December of 1776, with the might of the British military overpowering the Continental Army, George Washington appealed to the Continental Congress for more soldiers. With approval, Washington created additional regiments, commissioning Thomas Hartley as Colonel of one regiment.
Hartley was put in charge of recruiting soldiers for his regiment. On February 5th, 1776, Hartley chose Cox to serve as captain. One month prior, Cox had been offered a position as first lieutenant of Sim’s company. With the ability to rise further in rank, Cox ultimately joined Hartley’s additional regiment. 
In Hartley’s regiment, Cox, on September 11, 1777, fought at the Battle of Brandywine. The battle took place near the Brandywine creek, which crosses through southeastern Pennsylvania and northern Delaware. Hartley, along with the Continental Army and many regiments from Pennsylvania, fought against the British and Hessian regiments, who were ordered by British General Howe to encircle and incapacitate the American forces. When the enemy proved to be too powerful, Hartley and his men retreated to safety under the cover of the night.
During his time in Hartley’s regiment, Cox was able to partake in a triumphant charge against the British. At the Battle of Germantown, on October 4, 1777, Hartley, along with many of the Pennsylvanian regiments, ruthlessly attacked the British forces at Germantown road, forcing them to retreat.
Letter from William Smallwood, Calendar of Maryland State Papers, 1777, The Brown Books, MdHR 4609-82, 1/6/5/3.
In a letter from Colonel Smallwood on October 14, 1777, Cox and his men were viewed not only as the most behaved in the entire army, but also as the company that suffered the fewest desertions.
That December, Cox resigned, having lost his company due to lack of reenlistment. 
 Muster Rolls and Other Records of Service of Maryland Troops in the American Revolution, Archives of Maryland Online, vol. 18, p. 7 [hereafter Archives of Maryland vol. 18]
 Mark Andrew Tacyn, To the End: The First Maryland Regiment and the American Revolution, (PhD diss., University of Maryland College Park, 1999), 48-73.
 Tacyn, 48-73; “Extract of a letter from New-York: Account of the Battle on Long-Island,” 1 September 1776. American Archives, 5th series, vol. 2, 107
 Tacyn, 98-104; David Hackett Fisher, Washington’s Crossing, (Oxford University Press, 2004), 111.; “Extract of another letter, dated in the evening of the above day”, Maryland Gazette, November 7, 1776, Maryland Gazette Collection, Image 1202, MSA SC 2731.
 Robert K. Wright, Jr., The Continental Army, (Washington, D.C.: United States Army, 1983), 98-101.
 Compiled Service Records of Soldiers Who Served in the American Army during the Revolutionary War. NARA M881, Record Group 93, Roll 0077. From fold3.com; Compiled Service Records of Soldiers Who Served in the American Army during the Revolutionary War. NARA M881, Record Group 93, Roll 0397. From fold3.com
 Robert K. Wright, Jr., 117-119; Tacyn, 114-117; Thomas J. McGuire, The Philadelphia Campaign, Vol. 1, (Mechanicsburg, PA: Stackpole Books. 2006), 248-250.
 Thomas J. McGuire, 70-74.
 Letter from William Smallwood, Calendar of Maryland State Papers, 1777, The Brown Books, MdHR 4609-82, 1/6/5/3; “To George Washington from Colonel Thomas Hartley, 12 February 1777,” Founders Online, National Archives. http://founders.archives.gov/documents/Washington/03-08-02-0341