Thanks to their blue shield, warp ships are the spawners that are easiest spawners to spot from a distance, along with the Automaton bulk fabricators.
They are large circular structures with 2 thrusters in the back and a fin in the front. There are 2 doors on the sides of the warp ships, these are the weak points.
Warp ships are immune to normal weapons when hitting anywhere but the doors.
One strategy is to fire an explosive projectile at one of the doors after destroying its shield, such as:
The shield is very vulnerable to machine gun-type weapons:
You may also use red stratagems such as:
Assuming that the fire rate is at its maximum for all weapons, the average number of bullets required is:
30 for Stalwart
30 for Machine Gun
20 for Heavy Machine Gun
30 for Bullet Storm
In terms of speed, Bullet Storm is the fastest, tied with the Heavy Machine Gun. Then comes the Stalwart and finally the Machine Gun.
The most direct way to destroy warp ships is to use equipment that can kill them without having to destroy their shield first, or than can disable it very quickly.
The most common Orbital stratagems are listed below.
Eagle Aristrike and Eagle 500kg Bomb work as well but they're less consistent.
Rose for summarizing warp ship information.
Zovc for the warp ship icon.
Helldivers wiki for the warp ship image.