The most effective use of gunboat diplomacy

What was the most intelligent use of gunboat diplomacy?

Hornby's intervention at Constantinople in 1877, because it applied decisive force quickly enough to shape the crisis without turning it into the intended war.

Hornby's force worked because it arrived with clear purpose and was used before the situation spiralled into war. It was more than a visual demonstration: troops, ship placement, and intervention in the Ottoman command arrangement made the pressure operationally credible. Russia stopped short and the crisis did not turn into the British-Russian war that the fleet was meant to avert, satisfying Cable's test for successful limited coercion. A credible fleet presence and immediate practical action gave diplomacy a stronger position from which to operate.