Although knocking out their drives means a hull tanky ship it will need chaseing for 50km from the drop point as they seem to be-able to move faster than when they had drives. But even seekers so packs are more effective at taking out that annoying railgun or PA to make the ship just useless and just counting down their demise.
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Note there that the whole "packhounds kill weapons" is a bit of a bias. In the last beta we did plenty of testing there, and since missiles are not being changed, the results are still true: for the tast of destroying weapons on ships, seekers and packhounds performed very similar. For the first 18 seconds, which is 6 volleys of the seekers, both the direct damage potential as well as weapon damage is very similar. Packhounds have a small advantage, but it's not really significant. Only after 18 seconds packhounds really pull ahead. Seekers can fire one missile each three seconds till they have to reload, while packhounds right from the start go through the cycle of 1.5 seconds of fire-phase followed by 3 seconds of reload phase. So when the seekers get into their 12 seconds of reload time, packhounds keep firing. That is where their actual damage advantage comes from.
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So in terms of actual hull damage, packhounds are at a significant advantage due to better handling of reload time. But you don't need that many missiles to disarm a ship. On a FAS (one of the prefered testbeds) three seeker hits turned out to be enough to bring all weapons into malfunction state, while utilities failed even earlier.
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So the last potential difference are counter-measures. There are two things to look at, ECM and point defense. For ECM, even two of them are not sufficient to significally reduce a missile carriers damage output. It might be possible to counter torpedoes, but either missile launcher fires too fast and too often to allow ECM to really matter. But also note, due to the "fire/reload cycle" of packhounds" and their longer flight time (seekers fly direct and have slightly faster speed, packhounds fly a little slower and waste time by tumbling around), ECM actually is a little more effective against packhounds than against seekers.
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More interesting is point defense: when the attacker has only one launcher while the target has two PDS, then seekers roughly have a 50% chance to hit the target. Packhounds reliably deliver damage to the target in this scenario, but several of them are being shot down. It was hard to determine the exact number of packhounds destroyed, but it felt like of a salvo of 12, 4 to 6 missiles were destroyed, so 50% to 60% of the damage reached the target. When two launchers were in use, seekers rarely even lost one missile of the salvo. (The two PDS often seemed to target different missiles and failed to destroy even one before they impacted. ) Packhounds still seemed to have lost 4 to 6 missiles, no matter if 12 or 24 were fired. So if you have just one launcher and the target packs two PDS, packhounds probably are the better choice, but if you carry two missile launchers you might prefer regular seekers. It's also important to note that these numbers are based on tests with both ships being stationary and the missiles always being fired from a position where they were within the PDS firing arc all of the time. Range and speed differences, as well as the firing arc of PDS (which differs from ship to ship and even from utility slot to utility slot) can push these numbers in either direction, but the general weighting should stay similar.
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Mind you, this last two paragraphs were all about counter-measures. In terms of raw hull damage done the packhounds still win. It's just good to know that this is really not because they would be better in destroying weapons and external module and it's not because of being much better in overwhelming defense. They simply are vastly superior as they just can keep firing constantly, while seekers have a painfully long reload time. But if your goal is "simply" to disarm a ship once its shields go down, for many defensive configurations the seeker might actually be the better choice.
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That all being said, packhounds are way more fun to fire, both since they are reliable (no reload pause) as well as the tumbling swarm is just more fun to watch. So i admit, i stick to them, as the few configurations and combinations where they might be at a small disadvantage are rare, while their advantages come into play very often.

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