197
UK activists break into israeli weapons factory and smash it up.
(streamable.com)
Dive into the World of Insane Videos!
Rules
Unscrewing everything they can get to (and destroying the screws/bolts/fasteners) would also be very effective. It's easy to justify replacing destroyed equipment, but working equipment that needs to be thoroughly re-inspected for sabotage takes time.
It would also give you access to stuff that's much easier to smash up.