Because it's guns are unique variants of the H44 guns, meaning it has BB5 range and damage.

How come it is the slowest bb around bb4-5!?
I dun think it's fair to km when RN, RM, IJN is with high dps and good speed.
The advantage of range is just very little for bb5.

Fine, you tell me y should i use a ebb4.5 with 2.1 belf armor and 8 bulge in GB.
Why i dun use h44 instead of it?? (H44 with AA setup can still run 23/39 with 233 engine) 

All of the new EBBs of that tier are just as slow, the Missouri, the Shinano, the Jean Bart.  The RN EBB Temeraire runs 37, so your comparison to the normal EBB Vanguard isn't really fair since the J39 is in the same tier as the Temeraire, not the Vanguard.

Why are you using 2.1" of belt? You should run 0.2", or 0.3" at most. 0.2" is enough to halve torpedo damage.

You should continue raising any further questions in this thread by Rehor. I suggest you read the main content of the second post.

So your J-39 has great range + good reload + decent firepower + awesome AA - but its only as fast as a Temeraire (which it outranges) and if you armour the Temeraire which can only hold 7" deck, it drops to 34 knots. 

So where most have two pros and one con yours has more pros and 1 con and your still complaining. The reason it cant run like a H-44 is simple - its not a H-44, if it had gone fast it would have to lose range and then you would be on here complaining that its just like your H-41 and it hasnt enough range.

dun u know the range of L2 gun and h44 is so close but the fire power is different. 

Pros are only range + aa
Cons are speed but it is the most important one for using pulling, rushing
22/37 is much worse than 23/39
The gap between 22/37 and 23/39 is large.  (2knt differences at full speed)
becoz  fast bb3 run 26/44  =37+7knt=39+5knt 
           normal bb3, fast bb4 run 25/42 =37+7knt=39+5knt
           normal bb4 run  24/40 =37+3knt=39+1knt
           normal bb5 run  23/39 =37+2knt=39+0knt

The range of the L2 gun and the H44 gun is close, but it is wide enough for you to hit them without being hit back. Firepower means nothing if it doesn't hit.

Pros are not only range + AA, it also has good reload and an extremely consistant damage output as the player above has explained. Reload and damage consistency are variables that are just as important. Plus the ability to AA and blind your enemy is a crucial part of KM playstyle.

Pulling is not necessary when slingshoting right and keeping your enemies at range. KM is also not a rushing nation. This makes speed far less important in KM than you seem to think it is.


The current J39 gun (which is the same as the H44) can:
- Cripple that fast BB3 you are so worried about with 1 shot. (it is no longer a fast BB3)

- Cripple the normal BB3 and with 1 shot and with the same shot, take away all the SD and seriously damage the fast BB4 you are also worried about (with enough range for him not to touch you).

- Seriously damage the normal BB4 with 1 shot with enough range for him not to hit you and place the second deadly shot before he shoots you. And I will add that he will shoot you from a very bad position as he needs to pull in with his nose ahead to reach you, which will make his rear guns useless against you.

- BB5 will be a challenge, but 3 well placed salvos is all you need. 1st before they reach you, 2nd one when he makes his first shot, 3rd one very far from his range because his engine won't be working at full strength and yours will.

All this I will add, without the enemy knowing where you are due to your AA.

Sorry to say this, but if you are worried about BB3s with a BB5 range and damage, your problems are deeper than just the speed of your ship.

Seriously, KM nation is far more of a challenge to others than what you paint it to be. I know because I have played it for years. 

Mostly u said are in  ideal case.  Reload is good comparing to which nation !? (u wana said the shooting angle?) blind em by AA is easy in bb room but not easy in gb with fwcv room

In bb room is ok but  not in normal gb room.  EM bb could also slingshot which is just a normal skill. After em rush in their range, most of the advantage of j39 is nearly lost.