Just an ordinary crowbar...in space.
The crowbar is a strong, high splash damage melee weapon. As such, it can only be effectively used by certain characters such as Protection Assault, Fortitude Demolition and Mobility Recon. There are only two crowbars per campaign. One is always found just north of the crashed Delta-1 Transport Vessel in the Airlock, and the other can be found in the Apollo Research Lab just to the right of Dr. Bergmann. The crowbar has several off quirks because of its unique status as melee.
Somewhat obvious, but the crowbar cannot be reloaded, nor can it use ammunition of any sort. This technically makes it the most ammo efficient weapon ingame. However, because of its brutally short range it cannot often be used to full effect.
The crowbar is a much lighter and simpler weapon when compared to the bulkier rifles that most other weapons are. Because of this nature, players can switch to the crowbar almost immediately. This makes for interesting tactics such as engaging an enemy at range with a Flamethrower MK-3 or 590A5 Combat Shotgun then switching to the crowbar as enemies reach melee distance.
Marines' high tech power armor is totally immune to the effects of the rather unimpressive crowbar, as a result, the crowbar cannot physically damage allied units in any way. However note that it can harm most neutral objects.
Unsurprisingly, the Crowbar lacks any capacity to attack flying enemies. The sole exception being Perses. Because of this, it's wise to carry at least one other weapon that is effective against air units when carrying a crowbar.