The Frigate is the most advanced naval unit of its time! Its superior hull and long-range cannons make it capable of powerful ranged attacks while having strong defenses against melee attackers. The Frigate's vast capabilities allow it to not only completely dominate the seas of the Renaissance Era, but also to support land armies from the coast, attacking both units and cities.
A combination of Frigates and Caravels is able to bring down even the strongest defenses of coastal cities, if left unchecked. This is due to the hidden bonus vs. city defenses, which allows the Frigate to do (almost) full damage against walls! Concentrate Frigate fire to wear down the city defense, then finish it off with Caravels!
Over the centuries the frigate has evolved from a square-rigged three-master in the 1700s too small to stand in the line-of-battle to the fast guided-missile toting warship, nimble enough to avoid the really big ships. But the role of the frigate in naval warfare hasn’t changed: patrol and/or escort duties. The British Royal Navy declared a frigate to be any full-rigged “rated ship” carrying at least 28 guns on a single continuous deck; but despite the Admiralty’s best efforts to define a “frigate,” these came in all sizes and configurations, even ironclads by the mid-1800s. Modern “frigates” are frigates in name only; commencing with WW2, the label was applied to anything smaller than a destroyer. The introduction of missiles to modern naval warfare made frigates even more lethal, and cost-effective. Why build a blundering great battleship, or even a cruiser or destroyer, when a “cheap” frigate would do?