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. During this time, Bra'tac called C-4 "4-C" until he was corrected. (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")
During a rescue mission on board a hive ship, Lieutenant Aiden Ford planted several C-4 charges. After rescuing Sheppard, Sheppard ordered the charges detonated, causing serious damage to the hive ship and killing several Wraith, including Jimmy. (SGA: "Rising")
In 2004, when first meeting with the Genii, the First Atlantis Reconnaissance Team offered to trade C-4 in exchange for food. The Genii were interested in the explosive as they saw it as the key to their nuclear weapons working. Doctor Rodney McKay confirmed that the C-4 could in fact be used for such a purpose, causing the Genii to seek out a supply of it. During the Genii invasion of Atlantis, one of the goals of Kolya's strike force was to steal all of the Atlantis expedition's C-4. Doctor Elizabeth Weir later made a deal with the Genii for two of their atomic weapons in exchange for some C-4 during the Battle of Atlantis. (SGA: "Underground", "The Storm", "The Eye", "The Siege, Part 2")
In 2005, the rogue Lieutenant Aiden Ford and his men intended to use a C-4 charge in the Dart Bay of a hive ship in order to destroy it, one of many problems with his plan pointed out by Doctor Rodney McKay. This plan ultimately failed when the team was captured by the Wraith. (SGA: "The Lost Boys")
While retaking Atlantis during the Asuran invasion of Atlantis, McKay had the team made up of himself, Lt. Colonel John Sheppard, Teyla Emmagan, Ronon Dex, Weir and Doctor Carson Beckett plant C-4 in the Atlantis shield emitters so that the Replicators would believe that their plan was to destroy the shield when the Daedalus arrives so that the ship could destroy the city when in reality, the team actually turned the shield into a giant anti-Replicator weapon. The Replicators disarmed the C-4, but were fooled by the trick. (SGA: "The Return, Part 2")
When the Odyssey is taken over by Replicators, Lt. Colonel Cameron Mitchell plants a C-4 charge to destroy their queen and draw the Replicators away from the Asgard computer core. After a fight with a Replicator-controlled James Marrick, Mitchell detonates the C-4, killing the queen and Merrick though a Replicator reforms itself out of Merrick's remains before the Replicators are all destroyed. (SG1: "The Ark of Truth")
During the Battle of M2S-445, Sheppard and Ronon use C-4 charges to destroy the hyperdrive on Michael's cruiser, stranding the ship over M2S-445 and knocking out power to most of its systems. (SGA: "Search and Rescue")
While rescuing Ronon Dex from a Wraith lab, Tyre showed the rescue team where to plant their C-4 for maximum effectiveness and demonstrated to Tyre how to use the remote detonator. Later, while trying to force the Wraith Commander to let them escape, Tyre drew out the detonator and threatened to destroy the facility and all of its research if the Commander refused to let them go. Unwilling to lose any advantage the research gave his hive ship, the Commander agreed to let the team go and Tyre promised to trade the detonator for his freedom once they were clear. After the rescue team got away in a Puddle Jumper, Tyre detonated the C-4, destroying the lab and killing everyone within, including himself. (SGA: "Broken Ties")
As part of a plan to evacuate the Balarians and Elson's people, Sheppard has Elson use Jervis and his men to lure most of the Wraith on the planet into a mine where Sheppard leaves a C-4 charge. Once most of the Wraith are within the mine, Sheppard detonates the charge, dropping a big section of the ground above on those in the mine, killing them and evening the odds enough for the team to take out the Wraith guarding the Stargate and escape. (SGA: "Outsiders")
- In an alternate timeline, Colonel Samantha Carter supplied Ronon's strike force with Earth weapons and C-4. During an attack on one of Michael's labs, Ronon and "Todd" planted the C-4 in an important part of the base before being surrounded by Hybrids. Once Ronon's men were clear, Ronon detonated the C-4, destroying the lab and killing himself and "Todd". (SGA: "The Last Man")