Remote detonator, or timer
C-4 is a powerful high-velocity plastic explosive created by the Tau'ri.
They are usually contained in block form, though the plastic itself can be molded into other shapes. (SGA: "Quarantine") The explosive is usually detonated if a detonator is placed into the C-4 and remotely activated, or placed on a timer. The destructive power of properly placed C-4 has proven very effective in fighting the enemies the Tau'ri have faced. Placing the blocks in key areas can destroy a Goa'uld Ha'tak vessel and even Wraith Hive ships, as well as blow open doors and destroy other key enemy targets. However, they are ineffective against Kull warrior armor and are somewhat ineffective to Tau'ri blast doors unless used with a second pack. C-4 is also used in A-M18A1 Claymore mines. (SGA: "The Last Man", "Broken Ties", SG1: "Within the Serpent's Grasp", "The Serpent's Lair", "Evolution, Part 1", "Reckoning, Part 2")
- The emphasis on C-4 being the single important thing the Genii would need to make their weapons is a simplification. A compressive explosive lens would be much more difficult to design -especially timing the many detonators required-, so simply having the plastic explosive would help only a little compared to the technical specifics regarding the design.
During the Battle of Atlantis, the expedition was able to trade C-4 for two of the Genii's experimental nuclear weapons, which were then used against the attacking Wraith ships. (SGA: "Underground", "The Storm", "The Siege, Part 2")
During Apophis' attack on Earth in 1998 SG-1 destroyed the two Ha'taks used by Apophis. C-4 charges were placed at strategic places on one ship, while the other ship was then moved close enough to the first one so that the resulting explosion destroyed both ships. (SG1: "The Serpent's Lair")
While under the influence of the Atanik armbands Jack O'Neil, Samantha Carter and Daniel Jackson used C-4 to destroy the cooling systems around the power core on Apophis' prototype Battleship. (SG1: "Upgrades")
Bra'tac called C-4 "4-C" until he was corrected.