[8] While Putnam worked as a millwright, he devoted his free time to self-education, studying geography, mathematics, and surveying.

There, Putnam surveyed and chartered lands along the Mississippi River, which the Crown was going to grant to veterans of the French and Indian War in lieu of payment for their service.

At the urging of William Heath, Putnam used his experience working with British military engineers during the French and Indian war to build fortifications in Roxbury and other locations that were critical to the siege.

Using Muller's ideas, Putnam devised a system for fortifying Dorchester Heights, overlooking Boston Harbor.

Putnam's success in establishing a fort in a matter of just hours took the British by surprise and left them in an untenable position, resulting in their evacuation of Boston by sea in the following weeks.

[2] In December, 1776, when the Continental Congress rejected his proposition to establish a national corps of engineers, Putnam resigned his commission.

His resignation was short-lived and he eventually joined the Continental Army and served under Major General Horatio Gates.

In 1779 Putnam served under Major General Anthony Wayne in the Corps of Light Infantry following the capture of Stony Point, commanding the 4th Regiment.

[20][21] He established the Company in Boston on March 3, 1786, together with Benjamin Tupper, Samuel Holden Parsons, and Manasseh Cutler.

[2] Its primary purpose was to settle the Northwest Territory, roughly the lands between the Appalachian Mountains and the Mississippi River, which was ceded to the US by Great Britain under the Treaty of Paris (1783).

[25][26] The territory had been historically occupied by Native American tribes, and more were driven west by colonial encroachment before the Revolution.

From 1792 to 1793, Putnam served as a brigadier general in Anthony Wayne's Ohio campaign against these Native American tribes, including Shawnee, Lenape and Seneca, who were ultimately defeated.

The engraving on the stamp depicts a map of the United States at the time with the North West Territory between the figures of Putnam (right) and Manasseh Cutler.

One of his grandsons, Catharinus Putnam Buckingham, served as a brigadier general in the Union Army during the American Civil War.