Tyranid Old one.

The great old one

I’m having problems defeating the Tyranid old one, I currently have access to admiral Spire with a Battle ships redemptor and Oberon, a space marine fleet with a MK1 battle barge and Strike cruiser and a space marine fleet with a MK2 Battle barge and a light cruiser. This is the immediate system any tips or ideas?

Have play repeatedly and am defeated each time

ridiculous as this might sound
board it to death
you wont hurt its hp fast enough but nids are incredibly vulnerable to boarding
ignore how much this breaks lore and just honor the chapter it until it dies

hide spire in a corner, spam marine LCs with launch bays and torps and easily kill it with boarding

So best to rebuild the fleets to light cruisers

yes, marines currently has a massively overperforming fleet of LCs
you can do it with cruisers too
barges will just get eaten by nids tho
once you are out of charges on your ships warp them out, guns are completely irrelevant in that fight
its all about exploiting nids weak boarding defense and marines overperforming boarding spam

I did that mission yesterday. I used as many plasma macros as possible, because they allow you to kite tyranids. I had Spire with the retribution and 2 overlords, an AdMech fleet with 4 tyrants and then another Imperial Navy fleet with 3-4 overlords. Personally I don't think that boarding is a good idea, because the ancient one has an ability that destroys all your ships morale if you go close to it. It also has 56 troop value, which means that before hulking it you have to do 168 troop damage, which is a lot. I stayed away from the ancient one and destroyed all other tyranid ships first. The ancient one has massive hp and that scream ability, but it is not very well armed, so it's not a big problem if it stays alive. Expect heavy casualties. Hope this helps and good luck 🙂

Had no real trouble with this mission
Actually my SM fleets suffered quite heavy looses

My IN fleet has quite a lot of plasma macro and torpedoes
As for every game vs Tyrannid I had all my ships with Lock On enabled and engagement distance set to the maximum possible
My ships were outside of the scream radius most of the time
The Ancient One was a priority 4 target. This way my ships would actually engage the true threat of the mission : the other tyranids ships
I spammed the Melta and vanilla torpedoes on the AO which is just a huge barely moving target. Used lighting strike whenever possible too on it

It finally died due to 0 crew left but it had only 300 hp left when it happened. The SM reinforcement came just to claim the glory as they barely got in range when the mission ended
I actually think would have lost less ships with my long range AM fleet

board it to death yeah, remember tyranids have turrets based on their shields, like 1 turret per 50 shields iirc, so you can actually use a disruption bomb to instantly take away all of its turrets (though they will regen if the shields are allowed to replenish) right before all your boarding torpedoes and assault boats get there