Warning: Power loss detected. Engine Core is offline. Engine Core power restored. Thermal Engine fueled, primed and standing by for your command. Command accepted. Commencing five second countdown. 5... 4... 3... 2... 1... Engine firing. Test firing completed with an efficiency rating of 96.7 percent. Warning: Fuel depleted. Engine Core is offline.— Ignition sequence in ArcJet Systems during Call to Arms

XMB booster engine is a world object in Fallout 4.


The XMB booster engine is a nuclear-powered propulsion system developed by ArcJet Systems to be used for the USSA's Mars Shot Project. Development began in 2075, before it had actually been given the contract by the USSA. In August of the same year, CEO Thomas Reinhardt convinced the USSA to award ArcJet the contract and promised to have it completed by July 2077, a year before the Mars Shot Project was planned to launch. In the next month, Reinhardt would hire Dr. Rory McClellan, a military contractor, to lead the project.

In March 2076, Dr. McClellan reported that the booster was a few hundred tons over the strict weight guideline set by the USSA, setting the project back a month. In July, the USSA announced the Mars Shot Project to the public and began its public relations campaign, forcing CEO Reinhardt to lie to the press about the progress of the booster. However, by November Dr. McClellan was able to solve the weight issue, it now being seventeen pounds under the limit, and began fixing it to the engine core for test firing.

At an unknown point, an R&D scientist proposed switching from uranium to deuterium for the engine, claiming it would yield a better burn-to-thrust ratio. While Dr. McClellan was impressed by the scientist's proposal, the company refused to extend the project the three months required to make the switch, as it would cost them millions of dollars.

In February 2077, preparations were being made for a photo opportunity for the XMB booster engine, when a photographer made it past security during a test fire. The test fire vaporized the reporter completely without Dr. McClellan noticing. In fear of the USSA canceling their contract and ArcJet going bankrupt, CEO Reinhardt had the death covered up.[1]


During the quest Call to Arms in ArcJet Systems, the Sole Survivor and Paladin Danse will make their way through the engine core where the XMB booster engine is located in order to find the deep range transmitter. After restoring auxiliary power to the facility, the Sole Survivor can choose to activate the booster in order to vaporize a group of synths attacking Danse.


While the booster in the ArcJet Systems facility is a prototype G12, a prototype G10 can be found being hauled by a truck just east of the Greater Mass blood clinic. A terminal next to it allows for a test fire to be conducted, which will create a massive explosion and destroy the engine.