Gemini Rules for Warhammer 40,000.
These rules are now obsolete
Try the Gemini-ARAP 2.4 Rules

While the game rules in Warhammer 40,000 Rogue Trader (WH40K-RT) are quite good there always seemed to be room for improvement in certain areas. Having the likelihood of an Area weapon shot deviating determined by the size of its effect area rather than the shooter’s skill was one example that springs to mind. The Close combat rules also seemed a little too complicated. There were also possibly too many shooting modifiers, with some weapons being +2 at short range, -1 at long etc.

Recently I came across an old copy of the Warhammer 40,000 3rd Edition rules. I can see why some gamers don’t like these. I think the background etc in WH40K-RT is much better. There seems to be a drive to simplify things with 3rd Ed but it may have gone a little too far - Science Fiction fans like gadgetry and detail!

Both systems have their good points and bad, so it wasn’t long before I thought about trying to combine the two to create something that was easy to use but still fun and with plenty of flexibility.

This idea was to continually evolve and was eventually to become the Gemini ARAP System

If you look in WH40K Rogue Trader and compare it to more recent rulebooks you’ll notice something of a change in emphasis. Modern rules are mainly orientated around quite large armies. Permissible force structures are fairly regimented, as are most mission scenarios.

Rogue Trader was more orientated towards smaller skirmish-type combats. A wide number of story-line orientated mission scenarios and sub-plots were suggested and readers were encouraged to create their own. Not all of the suggested combats were between conventional military units or even using high-tech weaponry.

The suggested rules on these pages are orientated towards smaller and possibly more unusual combats as well as big battles.

My objective here is to create a game that is fast and easy to play. I hope to increase the character and detail of units without becoming bogged down with numerous “Special rules” or rules that don’t add anything to play.

Note that I’m not in anyway affiliated with Games Workshop nor do I in anyway intend to infringe copyright or discourage you buying the official rulebooks etc. You’ll actually need the rulebooks for some of the damage charts etc to use with these rules. I’d suggest getting a copy of WH40K-RT if you can find one since it has lots of good ideas for scenarios, creatures, weird terrain and the like.

Most of these rules are taken or inspired by those in WH40K-RT or 3rd Ed with some stuff from the 4th Edition. I’ve eliminated a few rules that I though were unnecessary complication and added a couple of my own. GMs are free to pick and chose to create what they think is logical. For want of any better term I’ll call these rules The Gemini Rules.

The Gemini rules are totally unofficial and should only be used in a game with the agreement of all players.


Other than your models and the rules all you really need is a tape measure, some templates/burst markers and some dice. A 6" Rule, 12" Clear Ruler and 3" piece of sprue will also prove very handy.

All of the basic game play is made with six-sided dice and I suggest you have plenty of them. Games Workshop shops have a very nice set of dice in a tin. You get twenty red dice, ten black and a Scatter dice and a couple of artillery dice (the latter not used in Gemini rules). Very reasonably priced a £5 and there is room in the tin to add a few more dice of other colours. Mine also has two white, two blue, two large green, one small green and a red and a blue D10. A selection of colours can be very useful when one or more models in a unit requires a different score.

A Scatter dice (left) has an arrow on four sides and a bull’s-eye/crosshairs on two. If you look carefully you will see that the crosshairs on the “Hit” faces also have small arrows (pointing to the right in the photo). When using a Scatter dice to determine a direction only this can used without the need to re-roll a Hit score. When a Scatter dice is being used to determine if a shot hits or scatters it is referred to in these rules as a Hit/Scatter dice. When it is only being used to establish a direction it is called a Scatter Only dice.

You can make a temporary Scatter dice by placing stickers on a normal dice. Some sites on the internet sell blank dice you can mark yourself. The bull’s-eyes go on opposite sides and when one is uppermost the arrow on each other face points at the top left corner.

If you own a set of Polygonal dice then you can establish Scatter Only by using a D12 and visualizing a clock-face.

Although not essential it is strongly suggested that the GM acquires a set of Polygonal dice. If you don’t have Polygonal dice a calculator that generates random numbers can be useful using some of the charts in WH40K-RT such as those for mutations or to generate psionic powers. One or two D10s and maybe a D4 is actually a lot quicker, however.

A few polygonal dice such as a couple of D10 may come in handy for some charts or randomly establishing casualties in a unit but are not essential.

If you are in London and do want Polygonal dice try Orc’s Nest just off Cambridge Circus. As well as sets of Polygonal Dice they also sell them loose so are the place to get extra D10s.

Blank Dice at Education Shop UK
Advancing Hordes Dice

Within these rules some dice rolls will be referred to as “Higher D6/D6". This means roll two D6 and take the higher value. Sometimes you’ll also annotation such as R4D6P2↑ or R3D6P2↓. The first means “Roll 3D6, Pick(use) the 2 highest scores”, while the second is read “Roll 3D6, Pick the 2 lowest scoring”. “Higher D6/D6" can therefore also be written R2P1↑.

Occassionally you will be called on to roll a D3. This can be done with a D6 and treating 1-2 as a “1”, 3-4 as a“2" and 4-6 as a “3". Some folks prefer to mentally halve the face value and round up. I find it easier to subtract 3 from any 4+ result. Use either method but make sure you opponent knows which you use and be concistent. If you need a D5 roll the same method is used with a D10. Advancing Hordes sold both D3 and D5 dice, and they may be found from some of their old suppliers still listed on their site. Be aware that if you use an actual three sided dice for a Swimming Roll you stand twice the chance of rolling a natural 1 and the model drowning!

Reaper’s Revenge are a useful source for D3s, D5s and other unusual dice. They also offer 12-sided dice with the sides labelled 1 to 4. These are somewhat easier to read than the isosceles tetrahedron D4s and apair may be useful for rolling variable moves for M4 units.


In the official WH40K rules distances are measured from the edges of the base. For a unit to be coherent there must be a distance of no more than 2" between models. This works if all the models have 25mm bases but does offer an unfair advantage to models with 40mm bases. With a 2" spacing far less models will be under a blast marker or template if on larger bases.

In Gemini rules unit coherency distance is taken to be 3" measured from the centre of the base. This means that models on 25mm bases are still placed with up to 2 between base edges but models on 40mm are placed with up to 1½" between base edges. Since 2" is two 25mm base diameters and 1½" is a 40mm base diameter this is all easy to set up. Measuring 3" centre to centre also allows the use of models mounted on other sized bases such as Warhammer 20mm square bases. A piece of sprue cut to 3" and painted bright colours (so you don’t loose it among all the other bits of model kit lying around!) will prove very useful for checking spacing. It is also useful for measuring the move of models on 25mm bases with a M of 4. Place the sprue with one end touching the edge of the base, then place the model so the rear side of the base is touching the other end of the sprue. This will be a 4" Move.

A clear 12" ruler will prove very useful for resolving shooting. Since it is clear any obstructions to the line of fire can be seen.

Leadership Tests.

Leadership tests are made against the model’s or unit’s Leadership (Ld) characteristic and are passed if the player rolls 2D6 equal to or less than the Ld. Some tests against Ld may be referred to variously as Break Tests, Morale Tests, Rout Tests or Rally Tests. This usually indicates a specific consequence that occurs if the test is passed or failed.Most Leadership tests may be taken against the Ld characteristic of the model leading the unit if this is higher.

Tests using Ld can be divided into several groups and it is important to appreciate the distinctions since some Units or Characters don’t have to take certain tests.

Tests to use Psionic powers and tests to fire against Chargers or other targets are taken by all units that have a Ld characteristic. Psionic tests use the Psyker’s Ld value. Some Psionic powers do not need a Psi-test to be made.

Rout Tests, Rally Tests, Shooting Morale Tests, Suppression, Last man Standing Tests and Tank Shock Tests are all Morale Tests and not made by Units that are Fearless or Dogged.

Test to use Special Skills (covered in the Optional rules section) are always rolled.

Pinning Tests caused by Pinning weapons are not taken by Fearless Units but are taken by Dogged, Stubborn and other Units.

Pinning Tests required from being in a vehicle that is damaged are taken by all units including Fearless.

Psychology Tests.

Psychology is covered in the Optional rules section. Psychology Tests are taken in the same way as Leadership tests but for some units are taken against the Cool (Cl) characteristic or Intelligence value when this differs from the Ld. Psychology Tests are taken against the lowest Ld or Cl value of the models present in the unit.

Units “Immune to Psychology” do not have to take tests, while some units always pass particular tests. Fearless units never need to take Fear or Terror tests, for example.

Other units are subject to Psychology unless specified.

Initiative Tests.

Initiative Tests are made against a single D6 and are passed if a value equal or lower than the Initiative characteristic is rolled. A roll of a natural 6 on an Initiative test is always a fail even if the model has an Initiative of 6 or greater.


Gemini rules games are intended to be fun for all parties so WYSIWYG restrictions do not apply.

The “What You See Is What You Get” rule appears on Page 167 of WH-40K 3rd Edition. I’ve not been able to locate this rule in the 4th Edition Rule book but it is repeated in some Army Codexes. Note that in 3rd Ed WH40K the WYSIWYG rule was clearly stated as not applying to grenades so you didn’t need to have grenades on your model for them to use grenades. The WYSIWYG rule states that any armament, equipment or upgrades held by a model must be represented on the model you use on the table-top.

For a well equipped character such as an Inquisitor it is obviously not practical to represent all of the specialized gear they may carry, or would result in an exceptionally ugly and ungainly model. Many models that have been produced by Games Workshop have equipment that is not allowed for by the Army lists. In practice WYSIWYG can lead to pettiness and bad sportsmanship. In Gemini games a combatant can have equipment not represented on the model providing the GM and other players are informed of this and the model can be clearly identified.

A Quick Summary of the Gemini Rules.

The Basic Gemini rules evolved out of Official WH40K rules, past and present so follow an “I go, you go (IGO-UGO)” format. The section below is mainly written for these rules but my prefered system is now the Gemini ARAP System. Currently I haven’t the time to update everything to ARAP rules, but it should be obvious how text written for IGO-UGO turn sequence fits into an ARAP Game.

To play the basic game you need to read the MOVEMENT, SHOOTING and ASSAULT phase pages. Each page begins with the basic rules and has more advanced rules, optional rules and special cases further down. Other pages describe more optional rules and rules specific to Vehicles, Buildings and Fliers.

Like the 3rd Ed rules the Gemini rules divide each turn into three parts, which are MOVEMENT phase, SHOOTING phase and ASSAULT phase.


One of the first differences that players will notice between Gemini Rules and Official 4th Edition WH40K rules is that different creatures have different move allowances. They also have a charge rate, which for the majority of creatures is twice the normal movement rate. Fall back rate is a third movement allowance which is determined by dice rolls every time the unit moves.

A human has a basic move allowance of 4" or a charge allowance of 8". Charging takes place in the movement phase instead of a normal move rather than being an extra move after the shooting phase.

Certain factors such as terrain type may have an effect on how far a model can move. Each inch of difficult ground that is moved through uses up 2" of movement allowance. Each inch of very difficult ground uses up 4". Making a turn of more than 90° reduces the move allowance by ½" for each additional 90° or part of. Moving backwards halves movement rate (ie each 1" uses 2" of allowance) and cannot be combined with running or charging.

Rules for jumping over gaps, climbing and swimming are given in the more detailed section on movement.

Most models operate as part of a unit and for the purposes of certain rules Unit Coherency is relevant. A model is coherent if it is within 3" or less of another model of the same unit. Note that under Gemini rules this distance is measured from base centre to base centre, not from base edges.

Like Warhammer and WH-40K-RT movement for charges takes place in the MOVEMENT phase, not after SHOOTING. I feel this makes it easier to keep track of what units can do what. Rules for charged units to shoot at chargers and some chargers to shoot at the units they charge are included.

Tests to Rally from Routs and to end Pursuits are made at the start of the MOVEMENT phase.

Rally tests are made in the routing player’s own turn. Tests to end pursuit are made in the pursuing player’s own turn.

If it is the player’s turn during the MOVEMENT phase each unit will be doing ONE of the following:

Routing, Pursing and Breaking Off are made at 2D6" for most troops.

Cavalry and Bikes make these moves at 3D6".

Dreadnoughts and Robots pursue or break off at their full normal movement allowance. They never Rout.

Traversing means the unit stays in place but can change the direction they are facing. In theory any turn of more than 90° uses the model’s movement allowance but most models have ample if they are stationary.

Keeping track of the traversing of stationary models is important if they have Heavy or Slow weapons. A Heavy weapon cannot fire in the SHOOTING phase if it traversed more than 90° during the MOVEMENT phase. A Slow weapon that traversed more than 90° can still fire in the SHOOTING phase as long as the firer was otherwise stationary.


SHOOTING phase uses the weapon profiles and rules from 3rd/4th Ed but using some of the modifiers from WH40K-RT.

To shoot at a target the target must be within range and visible to the shooter. How many times the shooter can fire and the range of the weapon will depend on the weapon type, whether the shooter has moved and conditions such as visibility.

SHOOTING phase uses the firer’s Ballistic Skill. The number of Attacks a model has in the profile is not used in SHOOTING phase and does not determine how many shots a model can take. To hit the target the shooter must roll against their Ballistic Skill (BS). A BS of 3 gives a basic 3 in 6 chance of hitting so a roll of 4+ is needed. A BS of 4 has a 4 in 6 chance so a 3+ is needed and so on.

Hits are randomized among the eligible targets within a unit. A roll of weapon Strength (S) verses the target’s Toughness (T) is made to see if damage is causes and the target may be eligible to make a saving roll to avoid the damage. If damage is caused and not saved the model takes one wound. If weapon strength was twice the target’s Toughness unsaved damage takes all the target’s remaining wounds and kills them outright.

If in a single turn a unit takes casualties of 25% or More of its current strength due to shooting or Psionic attack it must test for Morale.

Shooting rules for Gemini games are very similar to those for Official WH40K but use some to-hit modifiers for target size, speed, cover effects and other factors.One of the differences that will be most noticeable is that these rules do not use the Cover Save system but instead impose to-hit modifiers for cover.

Rules for using Area and Template weapons are a little different in Gemini rules. The shooter’s Ballistic Skill does have an influence of whether an Area marker deviates and high trajectory and indirect fire are made using guessed ranges. Ballistic Skill is also used to determine if a target under a Template is hit. Rules for using Hand-grenades in the Shooting phase are included.


I’ve made quite a few changes to ASSAULT phase, hopefully making it simpler but still exciting.

I’ve brought back the concept of pursuits and routs lasting more than one turn. One only needs to look at battles such as Marston Moor to see that victory can often hinge on the whether troops pursue or maintain discipline. On one flank the Royalist cavalry beat the Roundhead cavalry and left the field in pursuit or looted the baggage area. On the other flank the Roundhead cavalry drove off the Royalist cavalry, kept order and wheeled and charged the rear of the Royalist infantry.

Units not routing, in pursuit or breaking off in the MOVEMENT phase can charge an enemy unit. If a pursuit takes a pursuing unit into a new enemy unit this also counts as a charge. Note that charges are made at double rate while routs and pursuit distances are determined by dice rolls.

A unit charged has the option of Running Away or Standing and Firing.

To fight in close combat a model must be in base to base contact or within 3" of a friendly model in base to base contact with an enemy model. If for some reason a charging model doesn’t fulfill this condition at the end of its charge it cannot do anything for the rest of that turn.

A unit that charges gets an extra attack for the first round combat if it is entitled to fight an enemy.

Units in cover fight first, then in order of Initiative. Using “Frag and Charge” allows the charging unit to fight simultaneously with the unit in cover. Some situations may change a fighter’s Initiative.

Combat during close combat is made using the fighter’s Weapon Skill and he makes as many attacks as the Attack number of his profile. Certain situations or weapons may give additional attacks.

To hit, to wound and saving rolls are made. Casualties are removed

After a round of combat total of wounds is totaled up. Losing side tests for Rout. If the rout test fails the losing unit routs and is moved at the end of the ASSAULT phase. They continue to move in their next MOVEMENT phase until they rally, are destroyed or leave the field.

If the winning side doesn’t want to pursue it must pass a leadership test. If this is passed they spend their next MOVEMENT phase consolidating. If the result is pursuit it is moved after the routers at the end of the ASSAULT phase and in the Routers’ next MOVEMENT phase.

If the rout test is passed the two units prepare for their close combat in the ASSAULT phase of the next turn. Models that killed their foe are moved in base to base contact with new foes.

For convenience I’ll divide the rules into several sections.

Gemini ARAP Rules System




Extra and Optional Rules.

Vehicle Rules Section.

Building Rules

If you appreciate the efforts and time I’ve spent, feel free to buy me a beer. Cheers!

Warhammer 40000 Scrapboard Page

By the Author of the Scrapboard :

Attack, Avoid, Survive: Essential Principles of Self Defence

Available in Handy A5 and US Trade Formats.

Crash Combat. Second Edition with additional content.
Epub edition. Second Edition with additional content.
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