Incoming wall of text.
TL;DR: Add an "arming time" to all guns - unarmed shots deal ~80% of current damage, armed shots deal ~120% of current damage - and make ammo types focus more on modifying the armed range of the gun. This would fix gunners but possibly be too big of a change.
A lot of attention is being given to gunners and the lack of desire for gunners on some ships. Proposed buffs to the gunner class include new ammo types (supported by devs as the easy temporary fix), new gunner tools (supported by several players as a "real" solution), and altering the classes to carry different quantities of items (not heavily discussed yet).
I propose that these will not, and cannot, make the gunner any more desirable than it currently is.
Consider the pilot and his tools. He has tools that alter his movement speed. He has tools that alter his turning. He has tools that alter his vertical mobility. He even has a tool he can use to damage an enemy. A gunner or engineer trying to replace a pilot is insufficient in most cases because they don't have the variety of tools needed to do the job well enough - they can only carry one type of all these types of pilot tools.
Consider the engineer and his tools. He has tools that rebuild faster. He has tools that repair faster. He has tools that handle fire. He even has a tool that he can use to increase the damage of guns. A pilot or gunner trying to replace an engineer is insufficient in most cases because they don't have the variety of tools needed to do the job well enough - they can only carry one of all these types of engineer tools.
Now consider the gunner and his tools. He has tools that alter the way his gun deals damage.
That's it.
No matter what, the gunner tools in the current state of the game focus around the idea of optimizing the way you are dealing damage to the enemy. Greased ammo lets you deal damage faster in a single clip. Burst lets you deal damage in a greater area. Charged lets you deal lots of damage with a single shot.
When a captain designs his ship, he can select a certain way to deal damage for each weapon, and whatever crew member will be on that gun takes the ammo that best fits that damage style. No other ammo types are needed simply because they deal damage in a way that the captain doesn't need - it doesn't fit the style of his ship. A pilot or an engineer on a gun works just as well as a gunner in most cases because they can deal damage in the way desired with just their one ammo type.
Going into why the proposed changes won't solve this:
New Ammos
In theory, adding new niche ammo types will make a captain want to have those ammo types on his ship. However, we are still left in the situation where captains will design their ship in a certain way and one ammo type will deal damage in a way that is ideal for their style. Captains will still only need the one ammo type for each gun, making gunners no more desirable than before.
New ammos that alter the health of the gun have more potential. A captain might want that extra protection and not be willing to sacrifice the shiny ammo type that fits their style. However, normal ammo is still remarkably good, and the health boost ammo would undoubtedly have downsides to damage output requiring the crew to reload to be able to win a fight. The concept is interesting and has potential, but is still limited.
New Gunner Tools
The player proposed solution of adding new gunner tools similar to the buff hammer would, in theory, make gunners more desirable. A gunner could increase their damage output while also using one of the fancy ammo types that benefit their captain's style. However, this is defeated by both the utility of normal ammo and the ingenuity of captains. Why would a gat-mortar pyramidion take a gunner for a gunning buff tool when they could take 2 engineers - one with the tool and one with greased? Crews have already shown that they can handle taking care of each others guns in terms of buffs. Now you just have a buffgineer and a gun loading engineer.
Even in situations where crew couldn't assist each other like that, normal ammo in a gun is never a bad thing. It deals greater DPS than a few ammo types and has no drawbacks. An engineer taking a gunner tool and just using normal ammo wouldn't see significant drawbacks by not having more specialized ammo.
New Class Loadouts
Altering the number of tools taken by each class would maybe do the trick. It would be closer than the other 2 options. But it would be a big change and need a lot of coding. Discussions seem to touch on it then shy away from it, so maybe I will just leave it alone for the time being.
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There is a common theme in the problems with most solutions proposed. And the problem isn't that engineers are too good. It's that normal ammo is too good, or rather, that the guns themselves are too good.
Take for instance the gatling gun. You can shoot to the limit of brawling range and only get better as your enemy gets closer. You shred armor absurdly fast and allow for the 1-2 punch of the metamidion to be a thing. Greased ammo lets you shoot even faster and can often be used as the only ammo on the gatling gun. Even without greased, normal ammo does an excellent job of stripping armor. Why take anything but an engineer?
Now let's add a new mechanic, or maybe alter an old one.
Every gun gets an arming time.
An "unarmed" shot deals -20% damage of current production.
An "armed" shot deals +20% damage of current production.
Arming times and gun ranges are altered to allow each projectile for each weapon an armed range that naturally extends, depending on the weapon, anywhere from 50 meters to several hundred meters.
Current production damages on guns with an arming time would need extra attention and revision to determine a satisfactory resting point.
Yes, this sounds crazy. Yes, this is crazy.
Consider - a crew with no knowledge of what is going on will still deal close to current damage and will still be able to kill, albeit somewhat slower. A crew with knowledge of how the arming works will deal extra damage, but not exceedingly so. Between the two, the ship dealing armed damage should win, but the difference may not be enough to make up for a surprise attack or focus fire from the unarmed ships. Maybe the percentages would be looked at and adjusted, but the concept is there.
Now consider that all ammos are revised around the concept of range control. Lesmok gets a larger armed range, but much further out. Greased may get a smaller armed range much closer in. Charged can have a smaller armed range at standard distance with no clip or fire rate reduction. New ammos could be added that play with the range in different ways.
Looking again at the gatling gun. Normal ammo could have an armed range of 200-350 meters (arms at 200 meters, max range is 350). Lesmok ammo might then have an armed range of 400-600. Greased ammo could have an armed range of 50-150. Charged ammo could have an armed range of 250-300. A new ammo might give an armed range of 10-90.
Now consider this new gatling gun with an engineer. If your engineer takes greased ammo they can fight effectively at ranges of 50-150 and 200-350. That's not bad, but an enemy could get inside your range gaps with a better ammo and easily out-damage you. Your extra engineering capabilities wouldn't be sufficient to handle the damage gap.
Now instead take a gunner with the new ammo, greased, and lesmok. Your effective ranges are now 10-90, 50-150, 200-350, and 400-600. Suddenly your job as a pilot becomes much easier and more interesting. You can stay effective at nearly any range a comparable ship will be fighting at, and now you can coordinate reloads with your gunner to try to move into your gunner's effective range as he finishes reloading and simultaneously move out of your opponent's effective range.
This is a crazy solution, yes. It turns a lot of things upside down, and throws a lot of things out the window. It also makes gunner a much more interesting role since since they now can deal damage in different ways and at different ranges. A pilot or engineer can't match their utility on a gun because they can't maintain damage output over as wide of a range. It would take a gutsy, confident pilot to not take a gunner. You really think you can keep the enemy in a such a small window of damage?
A good gunner also becomes immensely valuable. The ability to judge ranges and communicate plans with the pilot to load the appropriate ammo would be prized, as their ships would out-perform others.
Is this the right solution? Is such a large change even viable with a game nearly 2 years old? Would it be too difficult for new players to grasp?
I don't have the answers to these questions. But I do know that I don't foresee any other changes really making the gunner as interesting as this would.