I decided to do a separate thread from the one in my signature, just for the warships. This was due to two factors, one being that there are sooo many warships, and the second being that unlike the other thread, in this one, I plan on using specific guidelines in the conversion process, in addition to trying to port the ship's performance over.
Contents:EscortsImperial Navy-Sword FrigateImperial Navy-Firestorm FrigateImperial Navy-Cobra DestroyerOrk-Ravager Attack ShipSpace Marine-Hunter DestroyerCruisersImperial Navy-Dauntless Light CruiserImperial Navy-Lunar CruiserImperial Navy-Mars BattlecruiserOrk-Kill KroozerOrk-Terror ShipSpace Marine-Strike CruiserBattleshipsImperial Navy-EmperorSpace Marine-Battle BargeThe sources I will be drawing on are:
- Fantasy Flight Games's Rogue Trader system
- Other FFG RPG products in they add any relevancy
- Battleflett Gothic
- www.Lexicanum.com
- ...and any other internet sources I come across that seem like they might be legit, including sometimes video games
- Just found Epic Armageddon has some ship stats for troops carried
Ranges and SpeedsSome numbers to start with:
- Battletech space hex: 18 km across
- Battletech space turn: 1 minute
- Battltech space extreme range: 50 hexes
- 40k FFG Rogue Trader VU: Indeterminate, between 1000 km and 100,000 km
- 40k FFG Rogue Trader space turn 30 minutes
Most 40k space systems purposely leave out the exact measurements of their abstract distances in their games. Several in fact outright state that this is intentional. The closest that any come to it is the FFG Rogue Trader system. Rogue Trader Core Rulebook pg 213: "The distance represented by a single VU is deliberately abstract and left open to some interpretation due to space’s vast size. However, a good guideline is a single VU equals roughly 10,000 kilometres." With a VU standing for 'Void Unit" and it being their abstract measurement unit. This is noticeably not the same as an AU or astronomical unit, used by astronomers.
They suggest 10,000 km, however, there are several places where rogue trader's rules do not treat a VU as a 10,000 km distance, so 10,000 is not a hard and fast rule. Most egregious in this are navigator and psychic powers, which tend to treat a single AU as closer to 1000 km:
- RT core rulebook: Gaze into the Abyss pg 179: treats 100 km the same as 1 VU .
- RT core rulebook: Void Watcher pg 181: treats 1000 km as same as VU, and treats 10,000 km as the same as 2 VU, and treats 100,000 km as the same as 5 VU.
- The Navis Primer pg 99 Control the Weak Mind: compel with it's range of 5m times psy rating, can control another ship's weapons at a range of 1 VU per degree of success on the check.
- The Navis Primer pg 99 Flash Fire: allows a psyker with the base telekinesis discipline with it's range measured in allotments of 5m to light an entire component of a star ship on fire at a range of 6 VU
- Deathwatch: Honor the Chapter, pg 49 Shadows in the Stars: Librarian can detect stuff in space at a range of 1000 km times psy rating. If that were measured in 10,000 km VU, he wouldn't be detecting much, and the power would be useless with the ship's sensors detecting things from much, much further away.
- Deathwatch: Honor the Chapter, pg 49 Darkness Gate: Works like a teleportarium in doing a hit and run strike, range measured in allotments of 500 km. If that were measured in 10,000 km VU, he wouldn't be going very far, and the power would be useless with a normal hit and run being more effective.
Battlefleet Gothic: Base of the ship's model represents an area of "a few thousand kilometers" No other definition is given for actual distances.
As you can see, even the system that comes closest to defining the exact measurement is deliberately imprecise. For BattleTech, this is not the case, 50 hexes times 18 kilometers times 30 minutes comes out to 27,000 km, which is the distance a Battletech Capital Missile can travel in a single Rogue Trader turn. This is 2.7 VU if we use the suggested 10,000 km, however, if we use the more likely 1000 km, it comes out to 27 VU.
In addition, an Arvus Lighter has a speed of "2200 Kph or 7 VU" in FFG's Rogue Trader. Meanwhile a BattleTech DropShip in system transit will accelerate at a constant rate of 1G, which is essentially an increase of 2 velocity per turn. At 30 minutes, a velocity of 60 gives our DropShip a speed of 64,800 kph, traversing either 6.5 10,000 km VUs, or many more if the VU is much smaller.
TL:DR
At sublight speeds, BattleTech ships can travel at similar speeds as warhammer 40k ships. BattleTech Projectiles also travel at similar speeds to 40k projectiles (even though there is a serious difference in effective range).
Conversion Rule: In the original Battlefleet Gothic, weapons ranges were measured in cm. Each weapons battery is either 15, 30, 45, 60 cm range. This corresponds nicely enough for me with BattleTech's aerospace range bands of Short, Medium, Long, and Extreme.
Battlefleet Gothic's ship speeds were also measured in cm, with most ship showing between 15 and 35 cm per turn. I intend to have these correspond with BattleTech speed, with 15 cm being the equivalent of a 1-2 speed, and every 5 cm increment will increase the BattleTech safe thrust speed by 1 point. Anything with speed below 15 cm, will be built to have station keeping thrust only.After getting around to building the Emperor Class Battleship, I had to make a choice. BattleTech's warship SI maximums are based on how fast you go, so the Imperium's battleships were going to have to choose between meeting the SI requirements I set for this conversion, or going much faster than I had previously indicated. I decided to make them go faster.
I decided on faster because I believed readjusting the speeds on the ships I had already don to a new paradigm would be easier and better over all than making the battleships have too low an SI. As such I am redoing all previous ships to the new way, which is a safe thrust of 1 per 5 cm the Battlefleet Gothic speed was.
Weapon Damage and Ship HealthConverting damage from one system to another is one of the difficult tasks, if you are trying for any kind of accuracy. I could only find two points of reference between the two. The first was that one of the Rogue Trader sourcebooks added rules for 'Atomics' and Interstellar Operations has rules for nuclear warheads. In both systems they behave somewhat similarly. The weapon has to hit and might not penetrate the armor, but if it does, it's gonna really make the target cry. Unfortunately, I don't have any data on how many mega tons each of Rogue Trader's warheads are, so I can't give a direct comparison. I strongly suspect that Rogue Trader's Atomics are much higher kiloton-wise than BattleTech's peacekeeper missile, judging by a comparison with the Nova Cannon.
The second point of reference was what happened with your ship met an asteroid. In Battlefleet Gothic a ship that flies through an asteroid field takes 1d6 damage from multiple asteroid impacts. An escort will be destroyed by 2 of that damage, while larger ships might handle it better. In BattleTech, a ship that collides with a single asteroid will take 1d6 capital damage time the MoF on the control roll with a +2 modifier. This needs an average of 7 if the piloting skill of the Warship is a 5. It wouldn't be too hard to have a MoF of +2, which would result in 7 or more capital damage, with an MoF of 3 being 10 capital damage. If we assume that the multiple impacts being suffered by the Battlefleet Gothic ships is 1 asteroid per damage, which you could look at in battletech terms as approximately 10 capital damage per 1 BFG damage.
If you can accept that conjecture based conclusion, then the 40k ships health become simple to figure out, as does the weapons damage each ship should be producing. At that point the next thing is armor. Armor in Battlefleet Gothic is essentially a percentage chance to not be affected by any particular hit, represented by a d6. It ranges from 1 hit having a 50% chance to do anything noticeable, to an 83 percent chance for the ship to not be noticeable. Eventually though, hits will get through and damage the ship beyond the armor. Personally, this tells me a few things. One that the ship needs enough armor that 1 "hit" (which we established is 10 capital damage) will not threshold the ship's armor, since it should take at least 2 'hits' to guarantee a threshold (or an effect through the armor). Better armor increases that threshold further. The second is that the armor on the ship needs to be pretty thick. I decided to represent this as using as a base the ship's maximum armor value, based on it's SI, and then for less than top-of-the-line armor values, simply remove the same percentage from that max, that the dice roll would make it easier to be effected: approximately 17% per tier.
The last part of this is shields. Each void shield can absorb 1 'hit' or approximately 10 capital damage. I decided this would be best represented by adding 5 to the ship's SI per point of void shield. This will not only boost the ship's survival when taking damage to the structure, but also boost the effective armor levels on the ship.
Conversion RulesLooking at the ship in Battlefleet Gothic, it's BattleTech SI should be 10 times the ship's Hit's Stat.
It's weapons load out should accommodate damage values based on 10 times the damage values listed in it's Battlefleet Gothic Stats.
Increase that base SI by 5 per void shield the ship has.
For armor, a 6+ armor stat uses max armor
with a minimum threshold per location of 40, a 5+ uses 83% of max armor
with a minimum threshold of 30, and a 4+ armor stat uses 66% of max armor
, with a minimum threshold of 20.
(Turns out doing the threshold this way was not going to work with doing the SI the way I was)Weapons Choices and TurretsWeapons Batteries
Most ships in Battlefleet Gothic don't use individual weapons, but instead, they use weapons batteries. While there are multiple definition of what a battery is between ground combat and wet navy, modern wet navy ships use it in a similar meaning as ground artillery, and so I am adopting that one. In this case a battery is between 6 and 12 guns. So each entry that calls itself a battery will be selected based on matching the necessary damage with weapons that can fit in a battery for it, and fire at the indicated range. Exceptions to this will only be made if it is not otherwise possible to meet it.
Torpedoes
Warhammer 40(k) ships can fire a variety of ordnance from their torpedo tubes. For this reason I plan on using AR-10 launchers, at a rate of 2 per 1 point of torpedo strength on the 40k ship.Plan changed. I will be using the torpedo types that correspond with the ship in question's torpedo range. Some will have subcapital missiles. Any that would be getting the extreme range torpedoes will have AR-10s.
Lances
These are invariably described as energy weapons, and they are strong enough to penetrate hulls by themselves. For this reason I am intending on using
Naval PPCs in these places, whichever I can get to have the appropriate range band.
Nova Cannon
BattleTech has no close equivalent. However, not counting the effects of the shell fired, the mechanics of the weapon system are similar to a mass driver, in that the weapon accelerates a projectile, and does massive damage. For this reason I will be using mass drivers where nova cannon's would be. The Imperium just has some really nice alternate ammo types for it.
Launch Bays
These mention how many squadrons they carry, and as such, I will simply have the number of bays on equal to the number of vessels indicated per squadron on the chart for it in Battlefleet Kronus (rogue trader system) on page 14. In the case of ships that have multiple types of carried craft, I will put that many bays on for each type. Fighters will be fighters and bombers will be fighter bays, while assault boats will be small craft bays. Some exceptions may occur due to factions using odd things as their bombers. The Space marine Thunder Hawks for example will not be using fighter bays, and neither will the Tau Manta Missile Destroyers.
Ships Without Launch Bays
Most 40k ships do not use anything like DropShips. So for the purposes of cargo transfer and passenger/crew ferrying, each ship has some shuttles as well. In rogue trader on page 11, it states how many such shuttles should be included, so I will be adding that many to these ships... If I can find an appropriate stat to base it on. Some of the larger ships don't appear in rogue trader, and as such I as I go I will attempt to determine a pattern to go by that can extend into those sizes.
Turrets
40k ships have generic turrets as anti fighter defenses.
They do not do enough damage to harm other capital ships, so for each point of turret strength, I am putting the coverage at 1 capital damage. By coverage I mean that 360 around the ship
should be able to do capital damage in anti-fighter weapons equal to the Battlefleet Gothic turret stat of the ship. This does not have to be perfect though, and depending on when you put them some gaps in coverage is allowed, as it makes for better flavor on a ship. For these purposes, 'Anti-Fighter' is being defined as any weapon that can either get the bonus for flak (LB-X AC, HAG), or otherwise has a bonus to hit (Pulse Lasers). Because these turrets are also used to shoot missiles down, they should have an equivalent amount of AMS: coverage of 1 capital damage per point of turret stat.
NEWSomeone made some strong arguments to me that I wasn't putting enough standard scale weapons on to properly represent the turrets. Each point of turret was a decent chance of driving off an entire 20-fighter squadron in battlefleet gothic, before they could do any damage. With the Rogue Trader book 'Battlefleet Kronos' we know these squadrons were upwards of twenty fighters. The conversion I was using for turrets was not even close to that. As such as have moved them up to the same same scale as the weapons batteries, basically ten times what it was, so rather than each point of turret equating to one capital scale damage, I am changing it to be each point of turret equates to ten capital scale damage. For the ships I have already posted, I am simply multiplying the weapons bays I put on there by ten, which results in cargo, fire control, gunner seats, and weapon bay changes, along with the requisite c-bill and BV changes as well.
I also multiplied the AMS/LAMS systems by 10 as well. In some cases this gives the ship some pretty ridiculous point defense numbers. However, I would like to point out that even the Emeror Battleship does not seem to have any wasted AMS. Despite being over kill on capital missiles, since each missile is engaged individually by AMS, you only need 12 capital damage from AMS to essentially negate any capital missile (providing you have the heat sinks or ammo to continue negating them of course), however standard scale weapons are a different matter. Standard scale missiles are engaged by directly comparing numbers between the PDS engaging the attack, and the damage value of the bay performing the attack. Since a standard scale bay can be built to have a maximum of 700 standard scale damage, a PDS bay is not completely wasted until you exceed 700 PDS defense in any one fire arc. Until then you are only exceeding what canon ships can throw at you instead of meeting the potential a designer could toss out. Since I myself have designed ships with over a thousand LRM 20s on them, I don't feel bad about putting this kind of excessive AMS on a ship converted from Warhammer 40k, since that universe is entirely about going overboard.
I am also adding plasma weapons, and standard scale missile weapons to the list of what I am calling "Anti-Fighter". Plasma for it's ability to throw fighters out of control via heat scale, and missiles because someone pointed out to me that they are generally considered AA style weapons (Also so I can justify having a bajillion AMS one these ships.
Ship ClassificationLike the rest of it, I plan on using designations as close as possible. I will be basing it off of a comparison between the the ship's name (Sword class Frigate), it's designation in Battlefleet Gothic (Oberon class says it is a battleship), or when all else fails, by the hull's designation in Rogue Trader, or on the Lexicanum. I will then try to have the ship weigh in at the appropriate amount, based on the chart on pg 10 of Strategic Operations. Some exceptions will apply to this. For example, Tau escorts have to be carried in on gravitic hooks, so I plan on making them Pocket Warship DropShips, instead of any kind of warship. I will still get them as close the all of these rules as possible.
As with all of my other design threads, anyone is free to post their own conversion, however, I would like people to stick with the rules outlined here. I would also be interested in if you have a different take on any points, as you might have better ideas than me on it. I hope to post the first one tomorrow.
