The Royal Navy at Shanghai watched Japan as well as China

Why did the Royal Navy become involved around Shanghai in 1927?

Chinese Nationalist pressure mattered, but British concern that Japan might exploit the crisis was a major reason for the naval presence.

Chinese Nationalist pressure around Shanghai formed part of the immediate setting in 1927. Chinese internal disorder was a familiar problem and did not represent the Royal Navy's deepest concern. British planners also watched for Japan to use the crisis as an opportunity for expansion. The deployment combined protection of British interests with an effort to deter Japanese opportunism.