When Britain began watching US naval power closely

When did the Royal Navy begin to worry about the US Navy?

Mainly in the 1920s as a strategic matter, though American ship design had already been an important technological benchmark during the dreadnought race.

Serious British strategic concern about the US Navy emerged mainly in the 1920s. Before that, American construction mattered as a technological benchmark rather than an immediate enemy fleet. In the dreadnought era, Britain watched American and Italian designs because a visibly more powerful foreign ship could undermine the Royal Navy's claim to lead in quality even while Germany drove the numerical race. British planners therefore faced two competitions at once: fleet numbers against Germany and technical prestige against other innovative navies. Measuring a foreign navy did not necessarily mean preparing to fight it.