Thomas replied to me:
> And yes, a grav tank with a jet engine for thrust would be worse than a
> landing helicopter. A Seaking helicopter has about 10 ton at its very max,
> requiring a rotor with a diameter of 19 m. When such a Jolly Green Giant
> comes down on an open plane, it is already no fun - and now assume this on a
> narrow street between houses! (Ok, the street could not be *that* narrow
> …).

Hello Thomas,

remember that contragrav allows the grav tank to maneuver on less
than full thrust. It has to overcome drag and inertia, not weight.
By comparison, a helicopter needs enough power to lift itself. In
the 4E rules, contragrav becomes TL^, which will allow many more 
grav vehicle concepts once a new Vehicles comes around -- in the 
default 3E rules, contragrav flyers are reactionless.

> And the tanks do not only need the jets for accelerating, they need is for
> braking, too (or you have to plan for an anchor …). So what will happen
> if there is a battallion of such tanks fighting in an urban area, when fast
> moves are necessary to survive? Or the other way round: what sense would
> make a tank (TANK!) that cannot fight in closer areas? Ruling the open
> plains might be done easier from above.

Or you should only take grav tanks into cities if you expect to
fight anyway, but not for routine patrols.

And Zan wrote:
> I think that we should ask if weapons still need turrets at that TL?

Hello Zan,

that would be TL13 Energy-Phasing Surface (VXii29). But Star Trek
does not use all that many tanks. 
 
> The tank may be a disc or a flattened sphere with no surface features
> that hovers on agrav, moved by vectored reactionless thrust, with force
> fields and beam weapons that can fire from any point on the surface.

Force fields are another good point, more on that below.
 
And Johannes wrote:
> I don't think they will just fight tanks. But i think it will be likely 
> that they also fight tanks. 

Hello Johannes,

the best anti-tank weapon is another tank? That was the US 
conclusion from WWII, but it might be because _their_ tank
destroyers were so bad. 

> I would consider it likely however, that there are tanks, built primarily 
> for other missions (propably with downward mounted guns, because most 
> targets will be there) and dedicated tank killer tanks.

I expect that grav tanks are designed to fly low. A design
that requires skylining is suicidal.
 
My thoughts so far:

* There is a continuum from grav tanks (direct fire, heavy
  armor, relatively slow) to grav gunships (standoff fire,
  relatively fast at the expense of some armor) and grav
  artillery (no direct fire, weak armor, lots of RoF and 
  ammo to saturate point defenses).

* A "default TL13" grav tank will use vectored reactionless 
  thrusters. Probably mega, or at least super. Ballpark one
  or two G accel, but speed is capped at 600 mph by the
  aerodynamics unless shaped force fields are used.

* At this TL, gunships might be space-capable, even FTL 
  capable. Space capability is free with thrusters, life 
  support, and avionics for fast atmospheric flight, and
  the power system for thrusters and energy weapons means 
  FTL capability needs just the drive itself.

* Grav artillery might have to compete with ortillery. If 
  you can park lots and lots of disposable missile pods in
  orbit, who needs arty? On the other hand, the enemy can 
  map prepositioned ortillery at leisure.

* Energy weapons doing 30,000 to 50,000 points of damage, 
  or less with an armor divisor. One penetrating hit and 
  the tank may be history. The VE179 confetti rule might 
  come into play.

* DR 50,000 on one face is possible, but that brings the 
  other faces down to a few thousand points of armor. 

* Point defense will be limited by the engagement speed of 
  the individual weapons. The game mechanics are pushed to
  their limits -- TL13 computers should be able to aim and
  fire in less than one second, but the rules don't really
  have that exception. A loophole is the 'walking the 
  burst' rule, which gives decent hit chances with the 
  second four-round burst. A RoF 16 point defense weapon 
  can fire four bursts, while a RoF 20 weapon is less 
  effective with a single 20-round burst.

  Still, the high DR means that little missiles, or medium
  MIRVed ones, won't work unless they're antimatter or 
  nuclear. Point defense has to stop big missiles, which 
  will be fewer in number.

* The VXii force screens are not effective, because their
  DR is proportional to the diameter. They're good for 
  typical ships, not tanks. 

  The exception is an outer layer for special effects, 
  like shaped/streamlined or stealth screens.

* VE93 force screens might work, but Vehicles doesn't 
  mention that location armor or slope effects apply to 
  them, so I assume they don't work.

* Doing away with the turret will be a major cost and 
  weight saving, or extra punch and armor in the same 
  budget. 

  If I take a turret, should the gun have an universal 
  mount, or can I handle that by rolling the vehicle?

I'm working on the 'supporting cast' right now, combat 
engineer and logistics grav vehicles.

Regards,
Onno
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