The Royal Naval Patrol Service (RNPS) was a group of people who helped the Navy during World War II. They were like super-duper navy police officers who sailed around the seas of the United Kingdom looking for bad guys.
The RNPS did a lot of different things to help the Navy. They used their boats to look for enemy submarines, which are like big underwater machines that can shoot deadly torpedoes. They also helped to manage convoys of boats, which are groups of ships that stick together for safety. The RNPS crew kept watch to make sure no bad guys tried to attack the boats in the convoy.
At the start of the war, many people in the RNPS were fishermen or had worked on boats before. The Navy taught them extra skills, like how to use weapons and how to find and destroy underwater mines.
Even though the RNPS wasn't technically part of the Navy, they worked very closely with them to protect the United Kingdom from harm. It was a big job, but they did it with bravery and skill.