The "Longitude Problem" refers to the challenge of accurately determining a ship's east-west position at sea. While sailors could easily find their north-south position using the North Star or sextants, measuring longitude was much more difficult. This was crucial for navigation, as even small errors could lead to ships being miles off course. In the 18th century, the British government offered a reward for a reliable method to solve this problem. John Harrison, a clockmaker, developed a series of precise marine chronometers that allowed sailors to keep accurate time at sea, ultimately enabling them to calculate their longitude effectively.