|There is more information available on this subject at Fougasse on the English Wikipedia.|
A Fougasse is an improvised weapon that generally takes the appearance of a barrel or tube that is buried about a foot beneath the ground. It has grenades or some other form of propellant in the bottom of it and can be filled with Napalm ("Fire" Fougasses) or spent shell casings and various bits of metal ("Shrapnel" Fougasses). They can be remote detonated, sending fire and shrapnel upwards, cutting down anything above them for up to several meters. Normally they are used to destroy ground targets, but during an engagement on the surface of Jericho VII, SPARTAN-II Blue Team led by John-117 used ten Fougasses to destroy five Covenant Banshees. John-117 activated it when the fliers were still close to the ground on a strafing run so the blast would hit them perfectly.