I was going to ignore it and leave it alone, but the more I read the sub the more issues I saw. 2013 submission, 600 mile range, and shooting thousands of Ultrachrome/Durasteel needles at 'just' under Mach 1 speeds. With a weapon like that you'd be able to kill every man, woman, and child in New York City from South Carolina. Realistically, those needles would shred anything smaller than a Scotcha Tank, including PC's.
Honestly, I don't know what would do more damage to a battlefield. A single barrage of those or the Vulcan Cannon from inside atmosphere. And it's not just the 'power' of the weapon that is a problem. It's that you can handwave the ammo onto nearly anything. Such as a gunship... An now you've got a few dozen gunships launching projectiles that are roughly as powerful as the Vulcan Cannon and have no hard ammo limits or realistic range limitations.
You could create a ring of gunships over an entire continent and just shell the city until there is nothing left but the HAS Shielded Citadel.
Which you could kinda do anyway with the fleet they've brought.... But they shouldn't be able to do the same level of damage with a few gunships and some handwaved ammo.