Flag signals use the International Code of Signals — a standardized system where each flag represents a letter of the alphabet, with many individual flags also carrying a specific, universally recognized meaning on their own.
Single-Flag Meanings You’ll Actually See
Certain individual flags are flown alone specifically because their standalone meaning is important and immediately recognizable:
- Flag A (Alpha) — “I have a diver down; keep well clear at slow speed” — flown by vessels conducting diving operations
- Flag B (Bravo) — “I am taking in, discharging, or carrying dangerous goods”
- Flag O (Oscar) — “Man overboard”
- Flag Q (Quebec) — “My vessel is healthy and I request free pratique” (health clearance)
These are genuinely still used and recognized today, particularly Flag A for diving operations, which vessels are expected to actively look out for and give a wide berth.
Flags Combined for Longer Messages
Beyond single-flag meanings, flags can be combined in specific sequences (hoists) to spell out words or convey coded messages from the International Code of Signals book — though this method of detailed communication has been largely superseded by radio for practical, real-time exchanges.
Why Flag Signals Still Matter Today
Despite radio being the primary communication method, flag signals remain relevant because:
- No power or equipment failure risk — a flag is visible regardless of electrical or radio system status
- Immediately visible to any nearby vessel, without needing to be on a specific radio channel
- Certain signals (like Flag A for diving) are specifically expected to be recognized visually, as a safety precaution independent of radio contact
Flags vs Morse Code vs Radio
All three are recognized maritime signaling methods, layered as genuine redundancy — flags for visual, close-range signaling; Morse code (historically, and still via signal lamp) for visual long-range; and radio for the primary modern method. Understanding all three remains part of comprehensive seamanship.
Exam Relevance
Common single-flag meanings (particularly Flag A, O, and B) and the role of the International Code of Signals are core Ship Knowledge and Signals topics in deck officer competency exams.