Warhammer 40,000: Inquisitor - Martyr

In the prophecy story campaign you're looking for the mission called tyranid menace. This once again has you piloting the crimson wanderer under Ambrose caradoc. If you've been playing on story mode setting. At the mission confirmation screen you need to press LT or RT and a marked box will indicate normal difficulty. Select +10 eye of terror and start.

One of the best things about this mission which is less prevalent in earlier tank missions. Is a) you can indeed crush most things by running them over. B) tyranids will swarm toward you,making running then over all the easier.
I honestly didn't need to die and try again. Even on +10. The tank missions for me required multiple deaths to hack through the level.
Here you have to go shoot to kill 4 large elite enemies called Toxicrenes ( cant crush these ones but you can crush any ads in the area if they either get in the way or start racking up significant damage on your knight.
Elite units, the carnifex are also roaming the map. These will require burning down with your weapons as these also cant be crushed but you'll want these killed to progress this achievement in addition to 4 mandatory kills of the toxicrenes (also elites)
Once the toxicrenes are dead, objective switches temporarily to a purge directive ( kill everything on the map) as you set about that a short cut scene will direct you to destroy the synapse. If this isn't happening just have a wander around purging (crushing) aliens until it does. The synapse will spawn in the middle of the map so head there. If you hang back you'll start to see a near constant stream of new tyranids rushing towards you in an overwhelming style from the malanthrope
Solution, just walk headlong into the synapse creatures (hormagaunts) to crush them. Then burn down the malanthrope with your guns.

The trick now which is described well enough elsewhere. Once caradoc roars "inquisitor! The swarm is no more" the mission complete box will pop up and you have the option to press the select button to finish the mission.
Press the xbox guide button on your controller and tab over to check your achievement progress. If you need more kills just come back to the guides home tab . Select the game tile for warhammer 40k inquisitor with the start button scroll down and select quit. Effectively crashing your game. Any in game xp or rewards from this level are lost but you keep your achievement progress. Reload the game and it will put you back on the bridge of ship ready to do it all over again.
Repeat as needed. Worth mentioning this also works for the "The emperors wrath" achievement where you need to complete 10 investigations on the highest difficulty. I found this level felt like less of a chore than doing the tank level in the base game.