“I have a diver down; keep well clear at slow speed.”
Signal structure
Alpha is divided vertically, white at the hoist and blue toward the fly, with a triangular section removed from the fly to form a swallowtail. Its shape helps distinguish it from the rectangular letter flags around it.
Operational use
The flag communicates a vessel-related diving operation, not the position of every individual free-swimming diver. Navigation rules may require a rigid replica at least one metre high when diving operations restrict a small vessel’s ability to manoeuvre.
Do not confuse it with
The familiar red field with a diagonal white stripe is a recreational diver-down flag used under national or local practice. It is not the International Code Alpha flag, and the two signals can carry different legal requirements.
Source trail
U.S. Coast Guard Navigation Center: Navigation Rules ↗
The International Code of Signals is maintained internationally; local rules determine required size and display circumstances.