say win here and one at fort funston. using telescopes, they named a ship and target. the two different sightings allowed them to trianglely position the ship at sea. >> so it was a lookout, essentially >> it was a lookout. >> i doubt if we saw a japanese ship today -- >> it would probably say toyota on the side of it. >> they are really fun. if shows you what can you do in 60 seconds. >> the pri sidot maps. people -- presidio maps. people keep forgetting that the army was a major presence. before the city was functioning, the army was functioning. and there are maps from the 1800's that show the farmhouses in the valley, the eureka valley, and mission district that were done by the army. so the army is its own resource for the history of the city before there was a building department. they would have everything. you could find out what was the original house in an area. again, this is the 1800's more than the 1900's. but the earthquake obliterated a lot of records. >> there's the survey map that the government did. that's a great resource to just kind of show -- you

december 7, 1941, this battery was finished and operational and there was a similar one by the zoo at fort funstonnd by noon on december 7, '41, soldiers were up here and they really thought that invasion was imminent. this is where the gunpowder was kept. >> reporter: john martini who helped restore this labyrinth of concrete and steel constructed more than 30 feet below ground, says at the height of world war ii, it housed more than 150 soldiers with rooms full of huge artillery rounds and enough powder to turn back a japanese naval attack. at the heart of it two big 16" guns that could sink a battleship with a single blow. the gun had a barrel 68 feet long. it could hit a target 25 miles out to sea. it would take about 2 minutes to get there. >> these are 16" caliber artillery projectiles and even up with was 2 ,100 pounds, each one. and it contains nearly 100 pounds of extremely high explosives. >> reporter: during the 1940s, the big guns roared to life often during practice firings and reportedly could be heard as far away as san mateo. >> you could hear the guns firing all over the bay area.

. >> reporter: the hardest hit, this stretch between sloat boulevard and fort funston where the greathway turns inland. >> we lost guardrail and the southbound lane. >> reporter: and that's just what the waves washed from the surface. look at this chart prepared by city consultants. here's the cliff in july 2007. here it is january 23rd, 2010, 50 feet inland. and just six days later, it's pushed back even farther where it ate into the southbound lanes of the highway. >> got cut off. >> reporter: but what's hidden under the surface is that circle on the chart. closer than ever to the crumbling cliff. that's a huge tunnel carrying rain runoff and sewage. >> 13 feet diameter. you know? can you imagine the size of your living room with a circle? >> reporter: this professional planner works for the city's department of public works. his crews closed southbound great highway and moved fast to save what was left of it and protect the tunnel. >> we're walking on the highway. >> reporter: the city abandoned the western-most pieces of the highway, rerouted lanes to the east, and dumped huge bou