Why not leave British trade protection to the United States?

Has the United States not been guarding British trade for decades, making an independent British contribution unnecessary?

The United States leads, but Britain still needs to contribute because alliances are stronger, more resilient, and more influential when every member brings usable power.

The United States has led much postwar protection of maritime trade, but Britain has remained an active participant rather than a passive client. Even a reliable ally cannot remove the need for national capacity. Alliances become stronger when each member can contribute ships, influence decisions, and help carry the operational burden. A state that relies on one power for nearly all of the lifting loses resilience and places both its security and political voice at risk.