Alright, so I just finish a 12 hour car ride alone....lots of time to sink into bordom and madness, but it go me thinking for one of my buddies black templar and how they can improve.
This is one of the idea I came up with
Althought to make some sense you would have to add barrage to the thunderfire shells to make it an indirect support unit.
Essentially it would turn the Thunderfire cannon into a directfire battle canon with the following shells.
Flakk round: Range: 60" S 8
AP 4 Type: Heavy 4, Skyfire
Sabbot round: Range: 60" S 9
AP 1 Type: Heavy 4, Overheat
Heat round Range: 60" S 9
AP 4 Type: Ordinance 4
Overheat: If you roll a 1 on a to-hit, you may not shoot with the ________ cannon next turn.
Special Rule:
Tracer rounds:Once you have declared which shells your are using you may make them Twin-link.
If you do so, until the beginning of your next turn, all enemies shooting at the __________Cannon
do so at +1BS. When night Fighting is in effects, units withing 24" may shoot normaly,
units withing 24"-48" treat the _____cannon as having the stealth specialy rule.
Crewed by a techmarine with a Techmarine upgraded with Servo Harness.
Cost 120pts.
If I were to make the new black templar codez (ha, yeah....long shot

), I would keep the devestator out of it, its simply not there style.
Giving them both the thunderfire and this ________ cannon would give them the long distance fire power to replace the devastator squad.
It would also give them a unique unit and make them that much moredifferent from the rest.
Fluff wise how can we justify them making black templar only: During one of there crusade they got push back by a massive armored Waaaagh to an ancient human fortresse,
in the depth of it they discovered an old rusted version of the cannon. Being assaulted from all side by orks tanks, with little to no anti-armored weapon
and the few thunderfire cannon with not enought fire power to punch throught armor. The Techmarine did the unthinkable and modified there own weapon to the newly discovered ___Cannon.
The new weapon prove effective.
They now keep this weapon secretly in there rank because both of awe at the effectiveness of the weapon and shame of its origine.
(this last bit of fluff I pulled out of my feth)
So what do you guys think?
P.S: sorr for any spelling mistake, english is not my birth tongue.