The design called for "a gun able to pierce a meter of steel, seven meters of concrete, or thirty meters of dense earth."
"... the entire machine stood 4 stories tall, 20 ft. wide and 140 ft. long. Moving, positioning, loading and maintaining this monster required a 500-man crew commanded by a major general.
"The Gustav's 800mm [approx. 2.6 feet] bore accepted two giant projectiles: a 10,584-pound high-explosive shell and a 16,540-pound concrete-piercing shell. ... the Gustav could strike targets up to 29 miles away." -Popular Mechanics