Question about symbols
 

Okay, it's high time that I asked this:

In SH3 I've seen the following symbols and inturpet them as such:

Triangle: Aircraft
Square: Merchant or Civilian ship
Diamond: Warship
Circle: Sub.

Now in the US Navy, we use the following symbols:

Ships:
Circle = friendly
Diamond = hostile
Square = Unknown

Aircraft:
Upper half of circle = friendly
Upside down V = hostile
upper part of square = unknown

Subs:
Lower half of circle = friendly
V = hostile
lower half of square = unknown

Obivously SH3 does not use these to get it down to the nitty gritty. But I am confused about something.

A small cirlce on my map will indicate a sub. A LARGE square normally indicates a Large Convoy, but so does a Large circle! I used to think that the large circle convoy's were friendly or allies, yet I've seen these leaving the coast of England!! ???

Can anyone explain what is going on?

Large circles in SH3 GWX are convoys shawowed by U-boats

Aye Brag is correct
The convoy has a uboat shadowing and radioing back position

That makes sense (sorta!). Thanks for the help guys.