Number of shots to destroy a vehicle:

Banshee - rocket x1, tank shot x1, shotgun x6, brute shot x4 (impact)
Ghost - rocket x1, gauss x1, grenade x1, sniper rifle x8
Scorpion - rocket x2, gauss x4 (body/tread), grenade x15, tank shot x2
Spectre - rocket x1, gauss x2, grenade x2, shotgun x6 (close)
Warthog - rocket x1, gauss x2, grenade x2, shotgun x6 (close)
Wraith - rocket x2, gauss x3 (front), gauss x2 (back), grenade x13, tank shot x2