I can infer that they are intended for aircraft to recognize the *Greyhound*, and for the *Greyhound* to confirm its identity. But do these code noun phrases signify anything more? They appear twice in [*Greyhound* (2020) - SCRIPT - Scraps from the loft](https://scrapsfromtheloft.com/2020/07/10/greyhound-movie-script/).

> 
> Message from the Admiralty, sir.
> 
> 
> Some of it’s badly scrambled, sir.  
> 
> I’ve done my best with it.
> 
> 
> XO to the bridge.  
> 
> Aye, aye, sir.
> 
> 
> What are these scrambles?
> 
> 
> I think coded numerals, sir.  
> 
> But I’m sure of that.
> 
> 
> “Expect aircraft.
> 
> 
> His challenge, ‘Uncle William.’  
> 
> Your answer, ‘Baker Dog.'”
> 
> 
> 

Second instance:

> 
> [lookout] Second sub spotted!  
> 
> Periscope, starboard bow!
> 
> 
> [lookout] He’s got us lined up, sir!
> 
> 
> All mounts, local control!  
> 
> Get those guns around!
> 
> 
> [lookout 2] Air cover! Air cover!
> 
> 
> [airplane propellers whirring]
> 
> 
> Signal Bridge reports aircraft signals.  
> 
> “Uncle William,” sir.
> 
> 
> Reply, “Baker Dog.”
> 
> 
> 

> 
> Right standard rudder!
> 
> 
> Mounts 41 and 42,
> 
> 
> open fire to mark the target  
> 
> for that aircraft!
> 
> 
>