It was created by Tallmadge (codename: JOHN BOLTON).

It would win the war, but it's existence wasn't revealed until 1929 by a letter. Not a single member was ever unmasked.

Numbers were used to code for a word:

example:

15 = advise

https://apps.dtic.mil/sti/pdfs/ADA566174.pdf

Upon his appointment as Commander-in-Chief on June 15, 1775, Washington immediately began efforts to build an intelligence capacity to assist in obtaining information on the British Army. He accomplished this by creating, directing, and managing spy networks, along with deception, and misinformation efforts in order to mitigate and offset the British military advantage. An additional benefit of serving in the British Army was Washington’s appreciation of their military capability. He knew at the outset of the American Revolution that he could not defeat the British Army in Europeanstyle warfare. This drove Washington to adopt a protracted, defensive strategy that leveraged all information and intelligence capabilities in order to offset the British tactical advantage.

General George Washington's victory over Hessian forces — or German regiments hired by the British — at the Battle of Trenton on December 26, 1776, ranks as an occasion where intelligence properly gathered and utilized secured a major Patriot victory.63 This victory was a result of the individual efforts of John Honeyman who was instrumental in providing General Washington accurate locations and dispositions of the Hessian forces. Early indicators of how Continental intelligence operations were improving was the Continental Army’s capture of Trenton in December 26, 1776.

Because the US army was outgunned in every way against the British, Washington decided the way to win was through psyop networks. Mess with their heads and know what they will do before they do it. This was the foundation of the US MIL intelligence network.

Initial success of the Continental Army was due in large part to the efforts of George Washington, Major Benjamin Tallmadge, Major John Clark, the Culper and Mersereau Spy Rings, and John Honeyman.

To the end of the war, the Culper’s flow of information proceeded—arrival and departure of British ships; British morale; British guesses about the peace; British losses in action; warnings against British agents in the American lines; maps and position sketches; exact location of individual units; quartermaster supplies; movements of British generals and other senior officers.81 This information, gathered by his network of agents, helped shape the campaign and allow him to fight and avoid battles throughout the American Revolution.

https://www.mountvernon.org/education/primary-source-collections/primary-source-collections/article/culper-code-book/

Example of its code:

kill 562

You could embed numbers in a letter and no one would realize that the numbers were a secret message.