Final answer:
In 1855, the United States Lifesaving Service was established, marking a significant development in the lifeguard profession. They were responsible for rescuing mariners in distress and ensuring maritime safety.
Step-by-step explanation:
In 1855, the lifeguard profession experienced significant developments. The United States Lifesaving Service was established in response to the increasing number of shipwrecks along the Atlantic coast. This organization trained and employed professional lifeguards to rescue mariners in distress. They played a crucial role in saving lives and promoting maritime safety.