What Did the Army Do Inside This Hill?

Soldiers moving an underwater mine with a fork lift.

Imagine the buzz of activity here in 1942 when army crews used this area to activate mines and then load them onto mine planting ships moored at today's fishing pier. The ships would then take the mines outside the Golden Gate and plant them in a semicircular underwater minefield surrounding the bay's entrance.

In December 1941, mine planter Captain Frank Liwski describes this activity...

"We worked day and night, cutting cables, and loading mines and planting them... Any vessel entering the harbor can not avoid our mine fields."

The mine depot structures built into the hill here reflect the dangerous aspects of this job. To avoid accidental explosions, the high explosives were stored in these underground concrete casemates to keep them cool and dark. In the room behind this wall, soldiers armed the mines by pouring granular dynamite into them. The dynamite was stored next door in Building 411, and the detonators were in Building 410, where you can still see the "explosives" and "no smoking" signs.