Vehicle House Rules

I mostly use the Spaceship system for vehicles in general and not just spaceships, these house rules when used together give a more cinematic and simplified result than just using the system as is.

 Useful Links:
https://samuelbaughn.blogspot.com/2026/02/gurps-spaceships-systems-index.html
https://gurb3d6.blogspot.com/2017/04/spaceships-quickie-power-cell-energy.html
https://gurb3d6.blogspot.com/2017/03/spaceships-quickie-spaceship-for-any.html
https://gurb3d6.blogspot.com/2017/03/spaceships-quickie-surviable-spaceships.html

Houserules

Relative Target Size; Harsher

Spinal and major batteries get -2 to hit per size difference between them and the target. -1 if they are secondary or tertiary batteries.

 

Chinks in Space

If you have an SM 5 smaller than your target, you may, after using a Sensor Analysis on the target, attack vulnerable parts of the targets armor, giving your attacks an increase in armor divisor just like chinks in armor for melee combat. This gives you a -10 penalty to attack rolls. This tactic does not work when using missiles, but it does work with torpedoes.

 

Survivable Space Combat:

dHP of all vehicles is doubled.

 

Scaling Gun/Missile Damage:

Use the table on the site for gun and warhead damage.

https://worldsbeyondearth.blogspot.com/2019/02/spaceships-how-much-damage-should-guns.html

 

Deadlier Beams:

All beams use the dDam2 progression; Plasma and particle beams have Armor Divisor 1 better.

 

Extreme Damage Variation:

Vehicles ST damage calculations are changed: Past ST 20, their Thrust and Swing is simply a number of dice equal to (dST/2) in Decade damage. Swing gets to add a +1 over thrust.

 

Keeping Large Vehicles Alive simple:

Piercing and Crushing damage is halved after DR and other modifiers against SM +6 or bigger ships.

 

Jump Boosts Simplified

Mecha  vehicles who have thrusters may use their thrusters in brief spurts to clear obstacles, and to increase their maneuverability. Instead of tracking delta-V and the number of G-seconds of thrust available, each mecha is given a number

of Jump Points equal to their delta-V reserves *60 in Earth-normal gravity. By spending one jump point, the mecha gains Super Jump 1 for the turn, two points gives Super Jump 2, four points gives Super Jump 3, and so on. Super Jump is capped to the G-acceleration of the engines being used. For reference, a smaller system composed of a chemical rocket and two fuel tanks provides 1G of acceleration and 0.1 mps of delta-V, or up to 6 uses of Super Jump 1.

Each level of Super Jump achieved increases your Thrust Rating by 1 and allows you to ignore terrain for the turn.

 

 

External Systems Simplified:

Mechas can carry extra systems of the same SM as external packs; one for each Hull section. Note that if you carry more than one external system, the mech will be at light encumbrance (Basic Move * 0.8; Vehicle Dodge -1).

 

Handheld Weapons Simplified:

Mechas can wield one weapon per arm, and may carry extra weapons as either cargo or as an external system.

 

Big Guns

If using two mechanical arms, they can carry a weapon of SM +1; but this encumbers them 1 level.

 

Two-Handed Melee Weapons: Treat two-handed melee weapons as if your dST was 1 category higher for the purposes of damage.

 

Tactical Combat Rules

Thrust Vectoring Owns the Sky: Mechas with a transforming ability may, as a Pilot Task, switch the side of their Vector Marker, switching its facing and location to be the opposite in relation to your own position.

 

Fasters Guns

Gun Salvo impulse is doubled.

 

Persistent Slow Missiles

Missiles Thrust Rating is halved and their burn points are doubled.

 

Long Range Beams

Beam range is multiplied by 100.

 

New System Options

Military Grade Armor:

You can double the DR of any Armor System, but the cost is Tripled.

 

Semi-Ablative Armor

Any Armor System can be made Semi-Ablative. Multiply the DR by 3 and the price by 3. This option is incompatible with Military Grade Armor.

 

Improved Compartmentalisation

Any Armor System may lose 1/3rd of it's dDR in order to give the section of the ship it's on Damage Reduction 2.

 

Space Torpedoes:

Space Torpedoes are space opera missiles. They're weaker than realistic missiles. This is a campaign switch; you shouldn't use torpedoes and missiles on the same campaign. Optionally you may say that past a certain SM, there's a switch from missiles to torpedoes. Space Torpedoes deal the damage of guns as if they were the next tier in the damage tables.

 

Anti-Ship Torpedoes:

These are Space Opera torpedoes that sacrifice targeting capacity for armor penetration; they can only target ships that are at least 3 size categories larger than their own ship. They have the same stats as Torpedoes but have an armor divisor of 4. They cannot be set to on airburst mode. Anti-Ship Torpedoes cost twice as much as regular torpedo batteries.

 

Simple Armor Facing

A spaceship may double the armor rating of one hull side; but must then halve the armor rating of the other hulls areas. They must have some armor on all sides for this option to be selected.

 

Sniper Weapon

A beam or gun can be made into a sniper weapon with double range but the rate of fire is reduced following the table below. Double it if the gun or beam is an "improved" weapon.

	20-second	1-minute	3-minute	10-minute
RoF	1*	1	3	10

*it can shoot once but must spend 1 round reloading. If it's an "improved" weapon its RoF is just 1.

 

Acid Spitter:

A "gun" type that deals Corrosive damage. Range is halved.

 

Mechanical Runners

All Mecha have Enhanced Move 1 (ground) for free. Upgrading the legs gives 1 extra level of Enhanced Move, and each level costs 50% 0f the leg price (so each level costs 50k for SM+4 legs)
 

Muscle Servomotors

This system enhances the Lifting dST and Striking dST of a vessel by a third of the difference between the dST of a Vessel of the SM 1 higher. Example: For an SM +5 mech, each Muscle Servomotor gives a bonus of +10. Max number of Muscle Servomotor system is 1. Beyond that just use Larger Systems to get bigger arms.

The price for this system is a third of the price of Robot Arms of the next Size Modifier. For example, for an SM+4 mecha, Muscle Servomotors cost 100k$

 

Combat House Rules

New Engineering Tasks

Divert Power

You may spend more power points on a system than it is rated with, increasing performance but at a risk of power surge. Make a skill check based on the skill used to repair the system. If you are successful, you may double the power used by the system, and increasing the effects of the system, depending on what kind of system it is.

• Reactionless Engines: Doubles the acceleration.
• Weapons: Increase Armor Divisor by 1 step.
• Sensors: While not usually systems that requires power, sending 1 Power Point to Sensors gives a bonus +2 to all skill checks involving Sensor Tasks for as long as the Sensor Array is consuming power.