Alpha flag
noun - An Alpha flag is a blue-and-white swallow tailed signal flag that is used under international maritime tradition and law. The International Code of Signals has established alpha flag to mean, I have a diver down; keep well clear at slow speed.
U.S. Coast Guard regulates its use in Rule 27e (Vessel Engaged in Diving Operations), "Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in this Rule, the following shall be exhibited:
Three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white; a rigid replica of the International Code flag "A" not less than 1 meter in height. Measures shall be taken to ensure its all-round visibility."
The alpha flag is established and recognized internationally for divers who are mostly below the surface of the water.
"To fly Flag Alpha" refers to when an escort boat is guiding an open water swimmer in an open body of water and indicates the presence of a channel swimmer or marathon swimmer in the water.
Synonyms
ALFA, ALPHA, A flag, I have a diver down; keep well clear at slow speed
