Based on the assumption you should run atleast 3 binds of ammo with L guns;

The lvl 54 15"/42 Mark I L fits on the Revenge with 3 binds.

The lvl 58 15"/42 Mark II L fits on the Renown with 3 binds, but on the Revenge with only 2 binds.

The Mark 2 compared to the Mark 1 does a good amount more damage, has more range, fires at the same angles, but has a 3 second longer reload time. But these advantages are probably because it is designed for the Renown, not the Revenge, and the Renown can only use 3 of them.

Rule of thumb:

If you have AT-LEVEL gunners (I suggest you level up your gunners from Lvl22 to Lvl65 and class them as Reload gunners directly; do NOT class them at Lvl42):

Always use 15*2 Mark I L, NOT 15*2 Mark II L, and switch to Mark III D AS SOON AS YOU CAN.

15*2 Mark II L shoots ONE SPLASH further than Mark I L, that's its only advantage over Mark I L guns.

Its disadvantages are:
1) 15*2 Mark II L gun is so much heavier than 15*2 Mark I L gun, which mean much less room for your armor.

2) 15*2 Mark II L gun has significantly longer reload time than Mark I L gun.

3) 15*2 MarkII guns have shell damage issue. I have seen Mark II shells bouncing "0" off none-armored ships in Blitz.

If you have lvl120 gunners, use Mark III D on these ships.

Thanks both for the replies.

Currently I'm using Mk I on both ships, I figure my gunners (level 61) are not good enough to have decent spread in Mk II (or Mk I for that matter), so extra damage is uselss, and my BO can barely see end of shells for Mk I, so extra range is also pointless at the moment.

As for classing gunner, I thought about delay classing because of losing accuracy, but searching the forums, most people advise classing on time for main gunners, as they will eventually cap both accuracy and reload. Sure, I suffer from terrible spread in blitz, but that's behind me and hopefully they'll get better. Also, if you don't class as heavy gunners at 42, I thought you can't use the 8'' CA guns?

I thought the Mk IIID have lower range than Mk I and II Ls, no?

I think Zorro might have meant the lvl 64 15"/42 Mark III normal gun, since this gun has BB3 range, I'm not sure if that range applies to all 3 Mark III guns. One of the problems you'll face though is that the guns greatly outrange your BO, so they often spread wildly.

As for classing gunners, you would indeed limit the guns available to you by delaying them. If you class full reload on time then your BB spread with EBVE gunners would only starting becoming truly workable around 70-75, and later for less accurate gunners. It can be quite late as UK gunners, but RN BB3 guns have high natural accuracy so you will see an improvement there, or on the KGV if you use that, at least until your gunners catch up to the cap.

Oh and btw, 15*2 Mark III D has [EDITED:] same or better range than Mark I L, but the gun is so much lighter than Mark I L (you can double check in GAME INFO->Components).

Mark II L is easily one of the best BB1 guns in the game.