San Francisco, as any local knows, is being besieged by an invasion force. The hordes' uniforms and accouterments are easy to spot: Horrible "Alcatraz Psycho Ward" T-shirts, ubiquitous maps, and guidebooks that lead them to Fourth and King when they're seeking Pier 39 with eerie regularity.
These international invaders are the lifeblood of the city. Much capital has been expended to look after then and keep them coming. More than a century ago, however, the government invested heavily in a project that would offer a different manner of welcome to foreigners. Specifically, it aimed to blow them up.
A frisbee's toss from Baker Beach at Battery Chamberlain sits the last
surviving remnant of the city's former coastal defenses -- a
107-year-old, six-inch artillery cannon that used to fire 100-pound
shells several miles.
The city's intricate coastal guns were meticulously maintained by thousands of men for decades. Yet their existence is a history of idleness followed by obsolescence. Unless the cannon teams were grumbling about their own issues, these guns were never fired in anger.
On the first weekend of every month, volunteer docents show anyone who straggles up how these big guns worked. If you tote in a laser pointer, incidentally, it'll be the only laser-guided element here. These guns were operated using the cutting-edge military technology of the Pythagorean theorem, slide rules, and chalkboards. Yes, speaking tubes were also involved.
If your brain evacuated all its knowledge of geometric practice after the SAT, don't feel embarrassed. Unlike a century ago, you don't need to remember this stuff to blow up ships anymore.
The Pythagorean theorem (you remember: A squared + B squared = C squared) allows one to calculate the length of the third side of a right triangle if you know the first two lengths. San Francisco gunners made it their business to know those two lengths. They knew how far away every landmark was -- so, that way, they could calculate the distance to a hostile ship.
Men with pencils would then meticulously work out the distance, flight time, and firing angle, and telephone -- or shout, if the power was down -- the coordinates to the gunners. This was as good as coastal defenses could get. In the 1890s, San Francisco was beefed up enough that it theoretically could have repelled an assault by Her Majesty's Navy. Not that the Americans thought the British were going to be landing on Baker Beach anytime soon. But the thinking was, if you can beat the best, you can beat the rest (the ocean floor was also littered with mines designed to force a column of water upwards and destroy the riveted hulls of the era).
The "disappearing gun" at Battery Chamberlain is built using a technology every bit as satisfyingly straightforward as the old-school triangulation methods used to fire upon its (nonexistent ) prey.
While it's hard to make a 97,000 pound object disappear, the cannon did just that. The recoil of firing a shell pushed the barrel back behind the parapet -- enemies would have seen a flash and a puff of smoke, but wouldn't have been able to eyeball what, exactly, was firing at them.
The recoil dropped the gun below its fortification into loading position. After two men packed in the 100-pound shell, a massive counterweight was dropped into a 12-foot pit beneath the cannon. This sprang the gun back up into firing position. Maintaining these guns was no mean feat; a number of the youthful gunners had engineering degrees -- and the dry job market of the late 19th and early 20th century ensured a goodly number of college boys joined the army. Quite a few of them spent their enlisted years practicing diligently to repel an invasion that would never come (and, considering the deterrence the guns presented, was always an unlikely possibility. Hypothetical invaders would do well to take, say, Ocean Beach, and then march overland toward downtown). Virtually every enlisted man who served on San Francisco's guns not only left his heart in our fair city -- but also his ability to hear clearly.
By the time of V-E Day, the city's coastal battery was long since archaic. Its susceptibilities were amply demonstrated in Manila, when the Brits' outward-facing guns were all but vaporized by a single plane dropping a single bomb that just happened to land in a powder magazine. Video killed the radio star, and air power killed the coastal battery.
Still, the "disappearing" guns remain part of the city's history -- and, certainly, the most exciting demonstration in San Francisco of the practicality of the Pythagorean theorem. Follow us on Twitter at @SFWeekly and @TheSnitchSF