Which military first used bugle calls and signals to relay signals and communicate instructions?

The Chinese military first used bugle calls and signals to relay signals and communicate instructions among its soldiers. They used bugle calls during the Korean War which happened in 1950 up to 1953.

It was said that the Chinese military use of bugle calls, which emitted sounds that were hauntingly unfamiliar to the American and Korean soldiers, is a form of psychological warfare that left said soldiers shaken and unable to defend their positions resulting to their deaths.

The answer to the question is a.

Transcontinental railroad was the most effective way to travel.