Boris Johnson reached for his life jacket as his election campaign ventured on to calm waters at the Port of Southampton.
The Prime Minister was joined by Home Secretary Priti Patel, and they were given a lengthy briefing before visiting a room where vessels are tracked.
While looking at the screens, Mr Johnson asked: “Where was it that they used to draw up the entire Royal Navy?”
A staff member noted “Portsmouth is on that side”, and confirmed this was the location of the naval base.
The PM later asked: “Can you spot the distinction between a vessel coming from the European Union or anywhere else?”
Ms Patel laughed at the question, while a staff member replied: “Erm, we can spot where they’re coming from geographically, as they approach.”
Mr Johnson and Ms Patel took a short trip on a boat to conclude their visit to Associated British Ports (ABP) Southampton.
The visit came as the Conservatives vowed to strengthen border security after Brexit.
Their choice of location for the visit is likely to have been influenced by the fact that Southampton Itchen was held by the party in 2017 by a majority of just 31 votes.