Component Hull Type Power Space SP Strength Damage Crit Rating Range
Torpedo Tube All Ships 2 1 1 1 1D10+4 3 6

Imperial torpedoes are as large as shuttlecraft but hit with the power of a dozen plasma bombs, the torpedo’s plasma propulsion acting as its warhead.
Torpedo Tube: Standard imperial ships may take two racks of torpedo tubes in their prow. Each rack counts as a separate weapon. You may take any number of torpedo tubes in each rack increasing the Strength by 1 per tube. The Space and SP of each and every subsequent tube in a rack is doubled from the previous. Ie a ship with 3 tubes in a rack gives up 7 space and 7 SP (1 for the first rack, 2 for the second and 4 for the third). If it took a fourth tube it would cost an additional 8 space and SP! Note that this means you are better off spreading your tubes across the two racks.
Ammunition: Torpedoes are so large that the strength of the shot represents the literal number of torpedoes fired. The space required for the torpedo tube includes 5 torpedoes. Additional torpedoes cost 1 space per 5 torpedoes.
Availability: Use the basic torpedo tube SP value rather than the compounded values for additional tubes.

Firing Torpedoes
These are fired as a Salvo. Choose the number of Torpedoes you wish to fire in the Salvo to a maximum of 1 per tube. Roll to hit as normal. Each Degree of Success indicates an additional Torpedo strike from the Salvo. When rolling for Damage roll 2D10 and pick the highest for each torpedo. If you did not roll enough DoS to hit with all the torpedoes it means the others have failed to detect the target and keep going in the same direction to their full range value.
Torpedoes continue along their ballistic trajectory until they hit something. Be sure to make a note of where the torpedoes are in relation to other objects in the area. After their initial firing, each torpedo salvo takes a single move action in a Strategic Round after everyone else has taken their turn. This must be their full Range value. If the torpedo salvo comes within 1 VU of any ship (friend or foe) the original firer must make a Ballistic Skill test to see if they home in on the ship, treating it in all ways as if they had shot at the ship. Fate Points can be used to automatically fail the BS test if the target ship is a friendly (representing excellent friend or foe programming skills). Keep track of the torpedoes until they leave the combat zone (usually but no always represented by the edges of whatever map is being used).
If the torpedo salvo moves through any celestial phenomena like gas clouds or debris there is a chance they will detonate. Make a BS test. Every DoS removes 1 torpedo from the salvo. As with friendly ships you may expend a Fate Point to automatically fail the test.
Torpedoes travel slow enough that they are not affected by Void Shields. Against Ghost Fields treat them as Lances.
Torpedoes and Turrets
Turrets come into their own against ordnance like torpedoes. Turrets are never commanded by a PC, there are too many of them spread too far across the ship. When a torpedo salvo strikes a ship the turret crew make a BS test (based on the crew skill of the ship). This is only against the torpedoes that actually strike the ship. The test receives +10 per point of turret rating. If the ship has 0 turret strength it does not have enough close range firepower to defeat any but the smallest ordnance barrage. If the ship has a turret rating of 0 no matter how well it rolls it can only ever destroy a single torpedo.
For every DoS the test makes it destroys a single torpedo in the salvo. It is not good enough to simply hit with the turrets, you must score 1+ DoS.
Detailed Method
Each turret does 1D5 damage. Each Torpedo has Armour 2 and Hull Integrity 0. For every DoS roll to damage the torpedoes, if the damage exceeds the armour the torpedo is destroyed before it hits the ship.
This leaves extra detail for specialised turrets with higher ratings and consequently more heavily armoured torpedoes to add more variety to ship construction and purchase choices.
Special Torpedoes
(with thanks to Andy Chambers for his Battlefleet Gothic special torpedoes)
The torpedoes above are the standard imperial plasma torpedo. They are easy to find and stock. There are rarer torpedoes out there however that have specialised uses. They do cost more however. The following is a list of rare types of torpedoes. These can only be bought singly one at a time. Unless otherwise stated these torpedoes use the same rules as those listed above.
Vortex Torpedoes
Availability: Extremely Rare
Vortex torpedoes carry warheads which implode to create a highly unstable and dangerous rift in warp space. The damage inflicted by even a single vortex torpedo is horrendous, whole sections of the ship and its crew are ripped asunder and sucked into the warp.
Hits inflicted by Vortex torpedoes automatically cause critical damage. If a ship which is carrying unused vortex torpedoes suffers a critical hit to its Prow (or wherever the torpedoes are launched from) it suffers an extra D10 points of damage and an automatic critical hit as the torpedoes detonate!
Melta Torpedoes
Availability: Very Rare
Melta torpedoes are fitted with multiple melta bomb warheads which detonate into mighty conflagrations of nuclear fire when they impact. The fires will burn through even the outer hull of a warship, threatening to consume the entire vessel in a hellish inferno.
Special rules
Hits from melta torpedoes inflict 1D10 damage and automatically cause a single Fire critical. If a ship which is carrying unused melta torpedoes suffers a critical hit to its Prow (or wherever the torpedoes are launched from) it adds 1 to the critical roll.
Seeking Torpedoes
Availability: Near Unique
The art of building self-guided torpedoes is almost lost to the Imperium but they are still manufactured at the great Adeptus Mechanicus temples on Mars. Logic engines and metriculators aboard the torpedoes themselves enable them to identify the attack vector most likely to result in the salvo reaching a target. The disadvantage of seeking torpedoes (other than their rarity) is that the surveyors seeking torpedoes use to detect enemy ships can be easily blinded by blasts and debris, leading to premature detonation.
Special rules
A Seeking Torpedo salvo will make a turn of up to 45 degrees before they move so that they are pointing towards the nearest enemy ship. If several enemy ships are an equal distance away the seeking torpedoes will turn to attack the largest enemy ship. Seeking torpedoes which move through debris cannot be prevented from detonating by using FPs. Unlike ordinary torpedoes, the superior logic engines onboard seeking torpedoes mean that they will not attack friendly ships that they move into contact with.
Guided Torpedoes
Availability: Very Rare
Guided torpedoes are directed via telemetry from the ship which launched them, allowing them to be guided onto targets or even directed against a specific enemy ship amidst the confusion of battle. Although tight beam communication links are used for control from the parent ship guided torpedoes are still vulnerable to enemy interference and jamming.
Guided torpedoes can make a turn of up to 45 degrees before they move if the player that fired them passes a Ballistic Skill test. If the test is failed one enemy ship can attempt to give the torpedo salvo false instructions by passing a Ballistic Skill test at -20. If the enemy ship is successful they are allowed to turn the torpedoes instead!
Short burn Torpedoes
Short burn torpedoes have more powerful engines but a limited amount of fuel. They are considerably faster than ordinary torpedoes but will ‘burn-out’ and lose engine power very quickly in comparison to ordinary torpedoes which are designed to cruise at speed for longer periods.
Short burn torpedoes increase their range to 8. However, they will only stay on the map for 1 strategic round before burning out and exploding.
A torpedo salvo occupies a single 'square' on the table, just like a ship. There is no way that you can spread torpedoes over multiple squares as technically they are all coming from the same tubes on the front of the ship which will be at most the width of the ship apart. So when firing torpedoes they will be spread across a 400 metre space from most ships.

If you aren't using squares, they would occupy a single 1" square (under the assumption that 1 VU = 1"). Torpedoes always travel in the same direction they were fired. When they reach 1 square/inch away from another ship (so 1VU) they test to see if they veer off and strike. Those that don't continue in the same direction, they don't change direction toward the enemy ship and keep going past it.

I'm not sure that individual torpedoes do enough damage. It's perfectly feasible for a ship to have a single torpedo tube, or just two. But 1D10+4 damage won't go through many ships' armour. A single torpedo should do damage to a Sword frigate, but with armour 18 it has more armour than the torpedo can do damage.
I was thinking of making torpedoes a bit like a combination of lance and battery. You roll a BS test to see how many detect the ship and hit it, and then roll a test for each torpedo that strikes. Each 2 degree of success adding an additional D10 to the basic torpedo damage. This would mean that although the number of hits is determined like a battery, the damage is determined more like a lance.
Or, to make it simpler, torpedoes ignore armour like lances or halve armour. However, if this were true their normal damage would have to change. a Spread of 4 torpedoes doing 1D10+4 each ignoring armour would do tonnes of damage to a ship in one go.
At the moment I like the idea of rolling to hit like a battery, but rolling damage levels like a lance.

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