How critical was John Harrison's marine chronometer to finding longitude?
Short answerIt was the first practical breakthrough and became foundational to the navigation that supported later British naval success.
NotesHarrison's marine chronometer was the first longitude breakthrough that truly worked in practice. Later solutions built on its principles rather than replacing the underlying need for accurate time. Reliable time allowed navigators to relate celestial observations to longitude at sea. The chronometer was therefore foundational to Britain's later operations in the Napoleonic Wars and its long maritime competition with France.