Kenneth Witt:
The GURPS Traveller Starship design rules allow for a single large fixed gun to be the major fore to aft structural element of a warship - i.e., a spinal mount weapon. Since bay weapons max out at 100 dtons and standard spine mounts start at 1,500 dtons, there is a large gap in capabilities between the largest bay mount beam weapons and the smallest standard spinal mount weapon. Destroyer class starships and similar sized system defense boats, which could make use of a gun with more range and firepower than a bay weapon, have no spinal weapons sized small enough to be practical. In order to address this need, I have designed the following weapons. These small spinal mount guns are suitable for use on warships with displacements from 2,000 to 6,000 dtons. Remember that the tonnage occupied by a spinal mount gun must be subtracted from the hull tonnage before calculating the number of turrets and/or bays that the ship may have. So each 100 dtons of spinal mount weaponry reduces the number of turrets allowed by one. For starships, a spinal mount gun that fills about 10% of the hull usually works well. System defense boats or battle riders often have spinal guns that use more than 25% of their internal volume.
Design Notes
Each complete spinal weapon system includes:
- Base Particle Accelerator or Meson Beam weapon with extreme range option.
- Full Stabilization for the beam weapon.
- A rechargeable power cell capable of powering one shot at the weapon's full rated power.
- A complete fusion generator (including core) capable of recharging the power cell in one minute.
- Long term access for the fusion generator.
- One roomy crew station for each 100 dtons of the weapon system.
- A computer terminal, HUDWAC, and pupil scanner for each crew station.
- A hardened dedicated Macroframe Computer (Complexity is TL-2), Targeting bonus is TL-1.
Weapons Tables
| Weapon Description | TL | Compact | Volume | Mass | Cost | Power (MW) |
| 62.9 GJ Spinal PAW/10 (x4) | 10 | No | 167 | 1,655 | 113.91 | 2,096.7 |
| 108.7 GJ Spinal PAW/10 (x5) | 10 | No | 287 | 2,859 | 196.42 | 3,623.3 |
| 212.3 GJ Spinal PAW/10 (x6) | 10 | No | 561 | 5,582 | 383.05 | 7,076.7 |
| 104.6 GJ Spinal PAW/11 (x5) | 11 | Yes | 180 | 1,552 | 258.39 | 3,486.7 |
| 222.3 GJ Spinal PAW/11 (x6) | 11 | Yes | 383 | 3,297 | 548.51 | 7,410.0 |
| 305.0 GJ Spinal PAW/11 (x7) | 11 | Yes | 526 | 4,523 | 752.35 | 10,166.7 |
| 62.9 GJ Spinal Meson Gun/12 (x4) | 12 | No | 167 | 1,654 | 103.14 | 2,096.7 |
| 108.7 GJ Spinal Meson Gun/12 (x5) | 12 | No | 287 | 2,857 | 177.84 | 3,623.3 |
| 212.3 GJ Spinal Meson Gun/12 (x6) | 12 | No | 561 | 5,578 | 346.81 | 7,076.7 |
| 104.6 GJ Spinal Meson Gun/13 (x5) | 13 | Yes | 180 | 1,551 | 258.14 | 3,486.7 |
| 222.3 GJ Spinal Meson Gun/13 (x6) | 13 | Yes | 383 | 3,295 | 547.97 | 7,410.0 |
| 305.0 GJ Spinal Meson Gun/13 (x7) | 13 | Yes | 525 | 4,520 | 751.62 | 10,166.7 |
| Weapon Description | TL | ROF | Damage | Half Range | Max. Range | Acc |
| 62.9 GJ Spinal PAW/10 (x4) | 10 | 1/60 | 5dx2000 | 32,445 / 3 | 97,334 / 10 | 35 |
| 108.7 GJ Spinal PAW/10 (x5) | 10 | 1/60 | 6dx2000 | 42,652 / 4 | 127,955 / 13 | 36 |
| 212.3 GJ Spinal PAW/10 (x6) | 10 | 1/60 | 5dx3000 | 59,607 / 6 | 178,820 / 18 | 37 |
| 104.6 GJ Spinal PAW/11 (x5) | 11 | 1/60 | 7dx2000 | 45,326 / 5 | 135,978 / 14 | 36 |
| 222.3 GJ Spinal PAW/11 (x6) | 11 | 1/60 | 6dx3000 | 66,077 / 7 | 198,232 / 20 | 37 |
| 305.0 GJ Spinal PAW/11 (x7) | 11 | 1/60 | 5dx4000 | 77,398 / 8 | 232,195 / 23 | 37 |
| 62.9 GJ Spinal Meson Gun/12 (x4) | 12 | 1/60 | 5dx2000(!) | 32,445 / 3 | 97,334 / 10 | 35 |
| 108.7 GJ Spinal Meson Gun/12 (x5) | 12 | 1/60 | 6dx2000(!) | 42,652 / 4 | 127,955 / 13 | 36 |
| 212.3 GJ Spinal Meson Gun/12 (x6) | 12 | 1/60 | 5dx3000(!) | 59,607 / 6 | 178,820 / 18 | 37 |
| 104.6 GJ Spinal Meson Gun/13 (x5) | 13 | 1/60 | 7dx2000(!) | 45,326 / 5 | 135,978 / 14 | 36 |
| 222.3 GJ Spinal Meson Gun/13 (x6) | 13 | 1/60 | 6dx3000(!) | 66,077 / 7 | 198,232 / 20 | 37 |
| 305.0 GJ Spinal Meson Gun/13 (x7) | 13 | 1/60 | 5dx4000(!) | 77,398 / 8 | 232,195 / 23 | 37 |
Note on Spinal Weapon Damage
All of the starship beam weapons in GURPS Traveller have been developed using the beam weapon design system in the GURPS Vehicles (2nd ed.) source book. The formula (VE2, p.125) used to calculate beam weapon damage includes the square root of the output power as one of its factors. This means that all other factors being equal, the weapon damage will scale with the square root of the volume of the gun. Defenses such as armor and meson screens that must spread their effect over the surface area of a ship will tend to scale up based on the cube root of the ship's volume. Likewise, the hit points of the ship are based on surface area and scale up much slower than the ship's volume as you go to larger hull sizes. The effect of the difference in scaling factors between offense and defense is that, if you set aside a percentage of the ship's volume (say 10%) for a spinal weapon, then once the ships increase beyond a certain size, the expected result of combat is that two opposing battleships will completely destroy each other with their first shots. In order to make fleet combat a little more interesting than that, a two part proposal was made to:
- Revise the damage formula so that power output above one giga-joule would cause damage based on the cube root of the beam power and
- Damage that penetrated the defenses would be multiplied by the cube root of the output in giga-joules so that on thin skinned targets the spinal mounts still had the one shot kill ability.
The first part of the proposal was adopted by Steve Jackson Games and the beam weapon damage formula was changed in the official errata for the GURPS Vehicles book. All the damage figures in the second edition of GURPS Traveller and in the table above were calculated using the revised damage formula. But apparently someone thought the second part of the proposed fix was too complicated and it was never included in the errata. Without the second part of the proposal, spinal weapons become so much less effective that their use on warships becomes very questionable. In one fleet combat play test where I participated, a smaller force of cruisers with heavy missile bays as their primary armament used their fighters as spotters and forward missile controllers and completely destroyed a larger force of cruisers with spinal weapons as their primary offensive weapons. The concentrated return fire from the meson spinal mounts proved ineffective and damaged only one of the missile cruisers. This convinced me that the second part of the proposal was essential if spinal mounts were to maintain their status as the primary offensive weapon for capital ships. So, for those of you who want to use the complete damage revision proposal, the number in parentheses after the weapon description is the multiplier (cube root of beam output in giga-joules) for damage that penetrates the target's defenses.
