In the 18th century, a humble English carpenter named John Harrison solved what was then the single greatest problem for seafaring nations.
For centuries, sailors had no reliable way to determine their longitude, their east-west position on the globe. This uncertainty led to countless shipwrecks, costing thousands of lives and fortunes in lost cargo.
The British government was so desperate for a solution that in 1714, it established the Board of Longitude and offered a massive prize, worth millions in today’s money, to anyone who could solve the problem.
Harrison was not a trained scientist or astronomer from a university. He was a self-taught clockmaker from a small village, a man of faith who believed he could build a timepiece that would stay accurate on a rolling ship. 
For decades, he labored, building a series of clocks known as H1, H2, and H3. These were large, complex machines, each one an improvement on the last, but still not quite perfect.
His breakthrough came with his fourth attempt, the H4. It was a beautiful and revolutionary device, looking more like a large pocket watch. It was compact, elegant, and brilliantly designed to withstand a ship’s motion and changes in temperature.
In 1761, the H4 was tested on a voyage to Jamaica. It performed astoundingly well, losing only a few seconds over the entire trip. Harrison had solved the problem.
But the academic elite on the Board of Longitude were skeptical of a simple clock from a country craftsman. They refused to award the full prize, demanding he reveal his secrets and build more clocks to prove his method wasn’t a fluke. 
After years of fighting the establishment, an elderly Harrison finally appealed directly to King George III, who declared, “By God, Harrison, I will see you righted!” With the King’s support, he finally received the recognition and money he had earned.
John Harrison’s invention, the marine chronometer, changed the world. It made the seas safer, gave the Royal Navy a huge strategic advantage, and ushered in a new era of global trade and exploration. 
Sources: National Maritime Museum, Royal Museums Greenwich, historical accounts