Isaac Doolittle (August 3, 1721 – February 13, 1800) was an early American clockmaker, inventor, engineer, manufacturer, militia officer, entrepreneur, printer, politician, and brass, iron, and silver artisan.

Doolittle was an important figure in the religious life of Connecticut as an Episcopal Churchwarden and co-founder of Trinity Church on the Green in New Haven.

Perhaps his most notable contribution is his having designed and crafted in 1775 the moving and brass parts for David Bushnell's submersible vessel Turtle, the first submarine used in combat.

He opened a shop across from Yale College on Chapel Street,[10] where he repaired, made, and sold not only clocks and watches, but "compasses, sea and land surveyors scales and protractors, gauging rods, walking sticks, silver plated buttons turned upon a horn, and a variety of other work".

[16] He designed an innovative nested bateau or lake boat for the 1755 amphibious attack on Fort Carillion and saw the construction of the Land Tortoise, a floating gunboat, skills he would use two decades later in the American Revolution.

[17] He also gained firsthand knowledge of British leadership incompetence in the disastrous expedition against Fort Carillon as well as their superior naval capabilities in the successful Siege of Louisbourg of 1758.

There he met the British Army surgeon Dr. Richard Shuckburgh, who composed the song Yankee Doodle while at the manor house in June of 1758.

He was selling imported silver watches, and advertising his own manufactured clocks, bar iron, "screws for clothiers"[21] and surveyor's instruments and mariner's compasses in his Chapel Street shop.

The Massachusetts Gazette and Boston Weekly News-Letter of September 7, 1768 described it as a "Mahogany Printing-Press on the most approved construction, which by some good judges in the Printing Way, is allowed to be the neatest ever made in America and equal, if not superior to any imported from Great-Britain".

It was said that the town always treated the casting of a bell as a great event, and many came to “watch the furnace being tapped and the metal flaming into the molds.”[26] His move from small metal casting to large may have been motivated by the need for arms in the coming war: given his experience as a field armorer, it was a small step from molding bells to molding cannons.

[36] In 1776, he was a member of the New Haven Committee of Safety,[37] where he organized a September 17, 1776, memorial warning against the activities of notorious Loyalists such as his fellow churchwarden Abiathar Camp,[38] who five years later in 1781 indeed procured pilots and boats to guide the British fleet into New London harbor.

According to Benjamin Gale, a respected doctor in the town of Clinton, Connecticut, and an inventor himself, the many brass and mechanical (moving) parts of were built by Doolittle.

Doolittle was a very wealthy and highly respected 55 year old head of a family of seven, a successful shop owner with a thriving business, the long time Warden and founder of Trinity Church in New Haven, and a pillar of the city, where he was a city and state armorer, tax collector, selectman, port inspector, lead prospector, and gunpowder miller with access to government funding.

In the context of the time, an "ingenious mechanic" in Gale's wording[47] was what today would be called an engineer and inventor, a designer and not just a craftsman.

[49] Given his wealth and public position, he also likely funded the Turtle's development, supplied the scarce commodities of gunpowder and lead, and obtained the colonial government's cooperation for the first tests.

[67] There is a humorous anecdote by the well-known New Haven physician Eneas Munson, a man known not only as a scientific doctor but for his droll comments at the expense even of his intimate friends, that may illuminate something of Doolittle's irascible character in this period.

According to the account of Henry Bronson: Doolittle continued to make clocks and cast bells until 1797, when his health failed again and he largely retired from business.

It has been noted that, "The talent of these local artisans and others ensured New Haven's reputation as a leading hardware and clock-manufacturing city by the middle of the nineteenth century".

Rick Brown, a co-builder of a 2002 replica, called it "the greatest technological advancement of the American Revolutionary War," and that with it, "Yankee ingenuity was born".

[80][81] For over half a century, from 1743 until his retirement in 1797, Doolittle was "one of the leading manufacturers and most versatile mechanics"[82] in the American colonies and "a citizen of character and enterprise, whose mark in his generation was that of striking originality",[83] as well as a key historical transition figure in the shift from Puritan to Yankee in New England.