"Palestine Action blockade weapons firm Thales' London offices, disrupting a lethal link in Israel's military supply chain," a statement from Palestine Action said. "We SHUT IT DOWN for Palestine!"
It also released video of the entryway being splashed with blood-red paint, with chanting of "Free, free Palestine!" in the background.
Similar attempts have been made outside the offices of the Elbit system, and its activists most recently occupied the entrance to the Leonardo armaments manufacturer in London.
At least 10,569 Palestinians have been killed in Gaza since the start of Israeli air and ground attacks 34 days ago, including 4,324 children and 2,823 women.
Aside from the large number of casualties and massive displacements, the Israeli siege is depleting basic supplies for Gaza's 2.3 million residents.
According to the World Food Program, food is running out and bakeries are closed in the Gaza Strip.
Since Oct. 21, at least 650 trucks carrying essential aid have entered Gaza, but people require much more, according to the UN humanitarian affairs office.