Having been informed that the cartouche is not a unique ship, and instead from the book of nemesis (meaning no new necron ships were made, and also that tindalos was super lazy and didn't give any of the non-armada ships their own models and instead of copy pasting over the model of similar ships) I will provide that lore.
Cartouche class light cruisers are light, fast, dangerous and - fortunately - rare vessels used by the mysterious
race known as the Necrons. In the Necrontyr's fleets, where these ships were observed, this class usually filled
the gap between typical cruisers and escort ships. They are not capable of fighting alone against cruisers or
battleships, so the Cartouches typical task is to hunt down enemy escort ships and engage light cruisers.
The most notably actions of these abnominations were destroying nearly the whole recon expedition during the
"157 Incident" and eliminating orbital defences around the Ellestratum Hive world, before the Necron invasion
known as the 797.M41 Ellestratum Massacre, or simply as the 'Great Harvest at Elles'
The report in the datacard below:
"... So we found this derelict ship, as we initially thought, floating within the asteroid belt, surrounding the inner, lone planet in system DHA 157/92. We were to investigate the belt for mining potential while the other
part of the expeditionary force was sent on to orbit the system's only planet to, as we were told, "assess it's capability for sustaining a fully operational mining colony". As the belt is positioned at an unusually large
radius from the system's sun, we expected some difficulties in communication. But we never expected to be forced to use it anyway, although long range scan of the belt indicated numerous, albeit weak and spread
out, energy emissions which were assumed to be some sort of radioactive material deposits. We could never be more wrong... The vessel appeared ancient and inoperational, however it somehow maintained safe
distance from every asteroid large enough to be able to damage it, altough we didn't realise it soon enough. We sent out probes to get images and radar scannings of the vessel, but the captain... Eh, he ordered
search parties to be sent... Eh, look - I don't know what he intended to achieve, but one after another teams were sent, through some sort of... bulkhead... we found by probe imaging of the ship's hull. Interior was
depresurised, so they all had to work in vacuum suits... They said something about... Bad feeling, fear, as they approached the alien vessel. Shortly after the first party landed we started having difficulties with
communicating with them, until we completly lost contact, but we assumed that it was the ship's hull which was interfering with our comunications, until a signal from one of the servitor's emergency beacon was
received. We sent another team to the rescue and... And we stirred up hell... Seconds after the second party reported that they would attempt to remotely undock the shuttle used by the previous party, a... I don't
know how to call it... a bolt of light... It shot straight out of the hull of this cursed thing and vaporised both shuttles! We didn't even have time to sound battle alarm, as what we think was the ship's main guns
spoke... The "Curious" research vessel was literally shredded to atoms by rays of green light; "Stubborn" was hit seconds later, at first comms just going silent, next minute the ship collapsed in a warp drive
implosion. We ordered a retreat, all ships setting all ahead full to spread out and escape from the belt. We tried to warn the second part of the expeditionary force, but couldn't reach them either by standard, nor by
astropathic communications... We took our chances and started running, limiting all comunications and emissions to a possible minimum, not to give our enemy a chance to lock on, but it seemed of no use - we
were hit thrice, captain being killed on the second... We tried to respond with fire but the enemy was almost impossible to target, as it would almost not exhibit energy emissions at all! I don't know if we had luck,
or did... they... just let us escape... We received comms from other vessels from our part of the force... They were destroyed... One by one... All of them... Only our ship escaped, barely... We entered the warp as
soon as we could... I still can see dark, glimmering slithouettes of those alien ships on nav screens... [longer pause] I'm sure all flight data will passed to appropriate persons... I... I don't know anything else... And...
I'm not going back there... [longer pause, followed by a shot]
Fragment of vox record of Second Officer Greg Thusk, o
ne of the surviors of "157 Incident", found dead at his cabin. Mission data records passed to Inquisitorial Authority. Unidentified class of Necron vessel sighted
on the vid logs and images. Class code named "Cartouche", cross ref. 1388463/2E7 "Kopesh" and 1388461 "Scythe" Expeditionary force dispatched to gather more data... "