Frankly speaking, RN DDs are not suitable for GB in new players' hands, unless you are quite good with NF already.
First of all, RN DDs cannot effectively AA like KM Z99;
Second of all, RN DDs cannot effectively play ASW as SN or IJN DDs which have incredible speed and numerous T slots.
Third of all, RN DDs are not small enough compared to RM DDs, so they are relatively easy to be killed.
If you have at-level crew, it is recommended to play RN DD in Blitz. Actually 2 RN DDs are quite good and recommended to be used in Blitz:
1) Level 16 Q Class (Remodel from Level 12 O Class)
and
2) Level 24 L Class
If your crew has low or no Vets/Experts, it is recommended to use Q Class until you have your first CL. Do NOT bother with Level 19 Tribal because it is absolutely crap. Use 4 inch dual on Q Class, and put as much armor as you can. Just get in range and fire at your enemy with your broadside. Q Class is one of the most hard-hitting, low-level DDs in Blitz. It also has 2 parallel T-slot which is nearly perfect for torping.
If your gunners have 100+ vets, you can start using L Class. Just mount the 2 front guns with 6 inch duals, and AW it. It's one of the most feared DDs in Blitz. But be sure to watch out for enemies' torps.
When I had high level gunners, I use L Class to play AA in GB, to level up new crew. I use 5.25 L and average at 2000 - 2500 AA credits per game. Again, it cannot effectively AA as KM Z99 but the experience you get from this DD will be more than enough to level up your new crew.
