Since I see similar inquiries across this forum regarding how to (late) class one's gunners, I am posting the screenshots of my gunners here.
Thanks to numerous events of 300% Vet Conversion Rate, here comes my final UK GB Gunner (based as Elite Repair, changed nation at Lv 12, leveled up all the way to Lv 101 and classed as Reload Huge Gunner all at once):
A pair of such gunners gives you over 6M repair true ability, which can save one Repairer slot of yours for one more Engineer. I believe other nations will benefit from late-classed gunners of this kind as well (with adjusted level of final classing of course; not necessarily have to be Lv 101 for all nations).
For WAW, it is recommended to get a pair of Lv 90 Special Neutral Sailors. You can class this pair of sailors to Armament Gunner, Gunner or Heavy Gunner before Lv 120. But make sure to make the final classing at Lv 120 to Reload Huge Gunner, in order to get the maximum free vets:
It is up to you whether to burn extra experts to get to 40% vet cap, but 296 vets with reload ability 4500 seems quite sufficient in WAW rooms (actually it kind of helps you slow down the rate you consume your ammo in WAW...)
Anyway, QV with such pair of gunners in WAW is real fun.