The attacks that ships make are divided into two sorts, direct firing and ordnance attacks. Direct fire attacks are weapons like lasers, fusion beams and plasma launchers which are fired and hit almost immediately even across tens of thousands of kilometres. Lances are incredibly high powered direct fire energy weapons capable of burning straight through an armoured hull or cutting an escort ship in two. On Imperial and Chaos ships lances are usually mounted in huge turrets with quad or triple energy projectors which focus into a concentrated beam of destruction.
Visually this would be along the lines of the advanced races’ weapons in B5, like the Minbari and Shadow ships - a coruscating beam of pure energy which is swept across a minute arc.
A lance turret would need to work something like this;
Immense power conduits enter at the bottom of the turret, feeding into house-sized capacitors and storage cells which form most of its base (ie magazine/ammo hoist area). The power conduits tap into the ship’s main power core, which in turn is energised by huge, throbbing plasma reactors.
The lance weapons themselves would be enormous energy projectors - each one the size of a factory chimney. They work by combining focussed coherent light (ie lasers) and electromagnetic pulses as a propellant for highly energised particles (ie plasma). The closest naturally occurring equivalent would be a solar flare but foccussed into a narrow beam. This means that lances would consist of a central particle/plasma chamber surounded by a series of enormous electromagnetic coils forming the barrel and muzzle, behind this would be a cluster of laser rods in the place of the breech/shell.
Other things in a lance turret would include;
bunk rooms, mess decks and a chapel for its crew (they would live eat, work and probably die inside their turret, never seeing the rest of the ship) -estimate around 200-500 gunners, officers etc.
Probably a tech-priest shrine (ie workshop/computer mainframe),
the turret winding gear and gun laying sections, plus engines and backups.
Stores of coolant to keep the turret efficient as it starts to heat up after a few shots.

inisfail.realmsofinisfail.com/bfg/bfg-lances.html

Iracundus wrote:

Hellebore wrote:
They fire like lasguns.

A Lance is not entirely around it being a beam - bombardment cannons are treated like lances and the warp cannons on Blackstones are as well.

Most of the time they are mega lasers though.

But they aren't lances in the same way lasguns arent lascannons

Bombardment cannon rules are similar but not quite the same as lances. Warp cannons on Blackstones were shield ignoring lances.

The fluff from Andy Chambers (who created BFG) from the old BFG mailing list seems to portray Imperial lances as more like a particle beam rather than lasers as we understand them:

The attacks that ships make are divided into two sorts, direct firing and ordnance attacks. Direct fire attacks are weapons like lasers, fusion beams and plasma launchers which are fired and hit almost immediately even across tens of thousands of kilometres. Lances are incredibly high powered direct fire energy weapons capable of burning straight through an armoured hull or cutting an escort ship in two. On Imperial and Chaos ships lances are usually mounted in huge turrets with quad or triple energy projectors which focus into a concentrated beam of destruction.
Visually this would be along the lines of the advanced races’ weapons in B5, like the Minbari and Shadow ships - a coruscating beam of pure energy which is swept across a minute arc.
A lance turret would need to work something like this;
Immense power conduits enter at the bottom of the turret, feeding into house-sized capacitors and storage cells which form most of its base (ie magazine/ammo hoist area). The power conduits tap into the ship’s main power core, which in turn is energised by huge, throbbing plasma reactors.
The lance weapons themselves would be enormous energy projectors - each one the size of a factory chimney. They work by combining focussed coherent light (ie lasers) and electromagnetic pulses as a propellant for highly energised particles (ie plasma). The closest naturally occurring equivalent would be a solar flare but foccussed into a narrow beam. This means that lances would consist of a central particle/plasma chamber surounded by a series of enormous electromagnetic coils forming the barrel and muzzle, behind this would be a cluster of laser rods in the place of the breech/shell.
Other things in a lance turret would include;
bunk rooms, mess decks and a chapel for its crew (they would live eat, work and probably die inside their turret, never seeing the rest of the ship) -estimate around 200-500 gunners, officers etc.
Probably a tech-priest shrine (ie workshop/computer mainframe),
the turret winding gear and gun laying sections, plus engines and backups.
Stores of coolant to keep the turret efficient as it starts to heat up after a few shots.

inisfail.realmsofinisfail.com/bfg/bfg-lances.html