In 1774 Portsmouth was, to all intent and purpose, a British sea port.  Not only was it a centre of commerce, mainly through its ship building, lumber trade and fishing, but the British also kept a large store of munitions in the poorly-defended Fort William and Mary on New Castle Island.  At a time when the British were trying to stop the import of munitions into the colonies it understandably became a potential target for American sympathisers. 

When Paul Revere rode north from Boston on December 13th 1774 with news that the British were sending ships with Marines on-board to garrison the town, his alarm sent nearly 40 men from the area storming through the garrison the very next day, dragging down the British flag before disappearing into the winter snow with over 70 barrels of stolen gunpowder.  The next day, further roused by word of Revere's message and the events of the day, a further group of men assembled in Portsmouth and returned to the fort to remove the remaining muskets and cannons. No lives were lost but these vital munitions, and the New Hampshire men themselves, later played a crucial role in the battle at Breed's ('Bunker') Hill on June 17th 1775.  The British presence in Portsmouth finally came to an end in August 1775. 

Portsmouth continued to be a major area of shipbuilding, and the celebrated American naval hero John Paul Jones (1747-92) spent time in Portsmouth on two separate occasions; the first in 1777 to oversee construction of the “Ranger”, and again in 1781-82 to oversee the building of the unfinished 74-gun "America" which eventually and, to Jones’ dismay, was gifted to the French as a replacement for the loss of their ship-of-the-line, 'Magnifique' that had recently run aground near Boston. 

In this chart Grant and Wheeler show considerable skill, both with their surveying and with their artistry, to present an informative and beautiful image.  On a point of accuracy it is worth noting that, according to modern satellite technology, Kittery Point has latitude of 43.0817 degrees.  In 1775 Grant, using only trigonometry and astrology, placed it at 43.5.0 degrees.