Final answer:
True, clocks that operated without a pendulum had to be invented before longitude at sea could be calculated.
Step-by-step explanation:
The statement is True.
In order to calculate longitude at sea, accurate clocks that operated without a pendulum had to be invented. This is because pendulum clocks, although accurate on land, were not suitable for use on ships due to their sensitivity to the motion of the ship.
John Harrison, a British clockmaker, spent decades trying to solve the problem of longitude and developed accurate clocks, known as chronometers, that were able to maintain accurate time on long sea voyages. His successful clock, tested in 1761, eventually won him a prize for his achievement.