Learning Semaphore
When Tower Bridge is about to open, the Bridge Driver communicates with the ship to check that they’re ready to pass through. To do that we now use radio but, back when Tower Bridge was first opened, radio wasn’t invented so they had to use semaphore.
Semaphore is a way of sending messages to people who you can see but are too far away to talk to. Using your arms (or flags), you can spell out words - each position means a different letter.