moved to tips and tatics.

for DD's SS hunting is the main role for them in a GB

you can with a sonar man use the CL for SS hunting too as well as AA

as for CA's that depends on the nation you play

Most cruisers can carry a scout.  Just sayin...

As said, sub hunting in GB is THE duty of a DD.   A DD with a sonarman and HHs is the way to kill subs and many a BB will be happy you are around.    Poping some smoke to cover a BB from incoming salvos from time to time will actually get you "thanks" from BB players who normally won't talk to anyone.    A BB driver likes to have an ASW shp around and some BB players will actually  ask you to team with them.   (Always do that and never abandon your team mate BB-do your job-cover him and stay out of his way.)

Don't forget that CVs are primary SS targets.  So on ASW patrol, you may have to run to the rescue of a CV.   They are VERY grateful when you kill a sub.   A CVs job is not running from an SS but handling their planes.

In addition to sub hunting, cover can be provided against raiding DDs hoping to launch torpedos into the main battle line.    Better that small ships deal with small ships so that your teams BB's can deal with enemy BBs.  

In later stages of winning games, you can carefully scout ahead of the slower advancing BB's to give them some vision.   Of course, this is very dangerous as the retreating BBs may see only the DD and target it hoping to blind the enemy.   Then again, the enemy BB may be so busy dodging the incoming salvos that he has no time to deal with a pesky DD.   The DD then becomes very valuable as the scout.    And from time to time, you will run down and sink an enemy CV or even a very crippled BB.
 
In GB, an ASW DD is a very important asset to the team. 

If you are trying to play GB then there is nothing for you but support roles really and thats the nature of the game. If you want to enjoy these ship classes in their gunship forms then blitz is your best bet for fun games though I would reccomend hosting yourself in order to play real maps as opposed to hobbit. DD/CL/CA type games do not go anymore and the general playerbase is afraid of normal room types.

There are many uses for CL/DD/CAs. In Blitz, DDs and CLs (mostly IJN) can play the role of the super annoying torp whore who runs to the front, releases the mother of all torpedo waves, and scurries behind the line, sowing discord and chaos before the game has really even begun. As said before, they can also be sub hunters in GB, although I prefer a CA, as the T slots can hold a ton of PHH. If you don't know how to use DDs, CLs, or CAs effectively in Blitzkrieg and Great Battle, you shouldn't be playing this game at all.