Rainbow Warrior would trigger a diplomatic crisis, not an Anglo-French war

How would France's sinking of Rainbow Warrior affect relations if the British Empire had remained powerful?

It would cause a much more serious diplomatic confrontation with Britain, but not a war.

The counterfactual asks how the 1985 sinking of Rainbow Warrior would play out if British imperial power had not declined. A stronger British response on behalf of New Zealand would produce a much larger Anglo-French diplomatic dispute. Serious anger would still fall short of a declaration of war over the destruction of a Greenpeace ship. The distinction separates the political gravity of state action against a civilian vessel from the much higher threshold for interstate war.