Which device is primarily used to measure electric current in a marine electrical circuit?

The device primarily used to measure electric current in a marine electrical circuit is an ammeter. An ammeter is designed specifically to measure the flow of electric current in amperes (A).

In marine applications, accurately measuring the current is crucial for ensuring the safe and efficient operation of electrical systems, helping to prevent overload conditions and electrical failures. The ammeter is connected in series with the circuit it is measuring, allowing it to accurately capture the amount of current flowing through.

Voltmeters measure voltage, ohmmeters measure resistance, and wattmeters measure power. While each of these instruments serves a specific purpose in electrical diagnostics, only the ammeter is used explicitly for current measurement, making it the correct choice in this context.