Gellar Field

The Gellar Field is a energy field that protects oneself and crew from getting a CLASS 10 CLUSTERFUCKING from Chaos. When traveling in the Warp. As everyone knows the only way to get anywhere without taking fucking forever is to use the Warp (unless you are an Eldar, in which case you can go much faster with webways as long as you don't get lost, or are Tyranids and can use gravitational Star Trek bullshit, or are Necrons and can screw the laws of physics seven ways till Sunday, or are Tau, who invent new less shitty then previous but still shitty non-Warp FTL drive like every 20-30 years), but as we all know all sorts of fucked up shit lives in the Warp whose ONLY goal is to fuck you up (both literally and metaphorically) in 57 different variations. The Gellar Field prevents this from happening so the Servants of the Imperium can go to your planet and kill your Chaos-worshiping ass!

The Orks use a similar device that focuses the power of the WAAAGH! into an energy field to keep the Daemons and other warp monsters away.

It involves jamming Really Big Teef onto the ship in an effort to frighten passing Warp-monsters. Hell yeah. Of course, if that doesn't work, the Orks will usually just give the unlucky daemons that tried to board their spacecraft a good stompin'. Either way, the Orks like both outcomes.